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What do you think a genderswapped Harry Potter (Harriet Potter?) would've been like?
So to start... I actually don't think life at the Dursleys would be all that different for Fem!Harry. Maybe there would be less *violent* bullying from Vernon and Dudley... but they honestly don't manage all that much as it is, and Harry's "normal" abuse mostly consists of being shouted at, locked up, treated as a scullery maid, and just generally made into a scapegoat + inferior/problem child that the rest of the family can unite around. If anything, Fem!Harry would have just reminded Petunia even MORE of Lily, and stirred up even MORE complicated emotions. And we'd get even more of live-in chef/maid Cinderella!Harry. It would all feel very Matilda.
The first big change I see happening... is I don't think Ron would have bonded with Harry on the train nearly as easily, if she were a girl. Young Ron is honestly pretty uncomfortable/awkward around girls... unless he's able to put them into a category like "little sister" (which doesn't count.) Or "know-it-all" (which doesn't count.) It's kind of a plot point in Book 4 that it takes him a while to realize Hermione and Ginny are girls he and Harry could potentially ask to the dance. Ron grew up around a bunch of guys, and you can tell. I think he'd try to *impress* Fem!Harry on the train, and probably put his foot in his mouth.
Harry would be at kind of loose ends on the Hogwarts Express, and get sucked into the search for Trevor the toad as something to do. So in this version, she actually ends up bonding with Neville. Hermione would be there too but well - Hermione rubbed Harry the wrong way at first in canon, and it would be even more the case here. They're both (functionally) muggleborn girls - but Hermione is SO much better prepared, and has SUCH loving parents, and won't shut up about any of this. In a way that Canon!Harry kind of fixates on Draco for ending up with his Ideal Life, it's possible that Fem!Harry might fixate more on Hermione.
11-year-old Draco would have treated Fem!Harry exactly the same, meeting her at Madame Malkin's and later on the train. He'd still have his obsession with her, and yeah, it probably does read as more of a crush to his Slytherin buddies... but I really do not see that stopping him. If his father can't get him to be normal to Harry, then that's just how it's going to be.
Harry will still get Sorted into Gryffindor, but I don't see her being close with any of the the other Gryffindor girls. Lavender and Parvati just have very different personalities, and Harry and Hermione... are very intense people who work best when they're able to take breaks from each other. In Book 4 when Harry is exclusively hanging out with Hermione, he comments that she's not as *fun* as Ron. And we see that dynamic again in Book 7 when it's just the two of them in the tent. Like they're incredibly effective, but seem to be wearing each other down a little. I think that forcing young (less emotionally mature) Harry and Hermione to be roommates would just end up with them getting on each other's nerves.
Hermione might get pulled into the friend group when Harry and Neville need help researching Nicholas Flamel, but she could easily stay more of a supporting character or even a frenemy in this version. Fem!Harry would still be the youngest seeker in a century. (Draco would be even more motivated to steal Neville's Remembrall if Neville is Harry's best friend... so that face-off would have gone down exactly the same.) Once she's actually on the team, I could see her falling in more with the upperclassmen, and hanging out with Fred, George, Lee, and Angelina (especially if they put together that she's a bit lonely.) It could be Harry, Neville, maybe Hermione, maybe the twins solving the puzzles at the end of Book 1. They'd still suspect Snape, who... would honestly be just a slightly different flavor of antagonistic and weird towards Harry, if she were a girl.
But in second year, Ginny would be Sorted into Gryffindor and I do think that Fem!Harry and Ginny would get along great, absolutely be bros. They could bond over quidditch, and Harry would get more of a sense of Ginny's actual personality (funny, cool). I have to think 11-year-old Ginny would be much less awkward around Harry if she were a girl.
Which would be really intense actually, because Ginny would have shown up to school with the the Diary, and it's... sort of important to the plot that she's isolated and has no friends. If she shares it with Harry as a cool thing - then Harry is ABSOLUTELY going to get obsessed with it. And since Harry's a much better *get* for Tom (Tom talks about being *so* pleased when powerful, important, future nemesis Harry starts writing to him instead of Ginny...) I think you just get Possessed!Harry opening up the Chamber of Secrets.
Also, would Harry have a crush on Tom? We know that Tom Riddle tries to impress Canon!Harry, which doesn't work... but Fem!Harry he might try to charm. Tom can be very charming if he wants to be. Harry also thinks he's very handsome. Either way, Tom is going to work VERY hard to to get Harry to distrust her friends. Really, you'd just get Harry's plot about being isolated and possessed by Voldemort in Book 5 moved to Book 2. Tom would get Harry to write "her skeleton will lie in the Chamber forever" on the wall, and lure her down to the Chamber of Secrets.
However. I do think that Lily's magic, which makes it impossible for Voldemort to physically touch Harry, would also make it impossible for him to properly drain her life and take over her body. I'm thinking of the moment at the end of Book 5 where Voldemort tries to possess Harry, but Harry fights him off. So... I think Harry just wakes up in the Chamber of Secrets with an intact Diary and a basilisk she can control, since of course she's still a parselmouth.
The question is... what happens to the Diary, now that Harry knows it's dangerous? I'm thinking that when Harry disappears, Ginny freaks out and tells one of her older brothers what's going on, who tells Arthur, who tells Dumbledore. Which leaves Dumbledore with a Horcrux that still works... and it seems like if you've got school-age Tom Riddle right there, that would be a much easier way to get an answer to the question 'how many horcuxes do you plan on making?' So Dumbledore gets a head start on that project.
Harry now effectively just is the Heir of Slytherin. She can go to the Chamber whenever she wants, and the basilisk is her familiar I guess (Hagrid would LOVE helping her take care of it.) I could also see a Harry who gets more *interested* in Salazar Slytherin after this. She definitely wouldn't talk to Draco - he spent Book 2 being an asshat and calling people slurs. But Harry might try to pick Theo's brain or something.
Now Hermione. At first I was thinking - does Hermione just die, in Book 2? Would she have known to look around corners with a mirror, and so survive her basilisk attack?
I do think she'd still figure it out... and it's because of Lockhart. Hermione is a Gilderoy Lockhart *fangirl,* and without Ron and Harry poo-pooing her crush (and without first hand experience of Lockhart causing issues for Harry...) I think she's able to geek about about this with her roomies. I mean, Lavender and Parvati read Witch Weekly. They know he's won the Most Charming Smile award. Hermione likes a project, and without Harry and Ron providing one, I think her new thing is impress Lockhart. And what would impress Lockhart? Well, he's a monster hunter who is trying to find the Chamber of Secrets and identify what's inside. How cool would it be, if they were the ones who helped him? He'd write about them in his next book.
So I think the Polyjuice Potion plan (Hermione's idea) is still a go. She might even talk Lavender and/or Parvati into helping out. (I mean, they joined the DA. They're up for some rulebreaking.) Hermione would still turn herself into a cat, which would actually massively humanize her in the eyes of her roommates, and I think they all end up much better friends in this AU. Eventually, one of them does manage to Polyjuice into Pansy, which is a much more effective way of interrogating Draco. And by this point, Hermione has met Myrtle, and has enough info to solve the mystery, and even bring her findings to Lockhart. Who ah. Finds an excuse to just run. There's a very fun portion of the year where Dumbledore teaches DADA.
I don't see all that much about Book 3 changing until the climax - because the crew Harry takes down to Hagrid's after dark *would* be different. Neville, Ginny (not the Twins - I think they give Harry the Map and peace out, they've got their own stuff going on and don't want to hang out with their much younger sister.) Maybe Theo? I could see him taking on a very Hermione-ish support role by this point.
But this also causes a problem, because if Ron isn't there, Scabbers isn't with him. And if Scabbers isn't with Ron - I don't think Remus notices Peter on the map, and so just stays inside and drinks his Wolfsbane, which means Snape doesn't go down. And since Sirius' target was never *actually* Harry... I think this is just a universe where Sirius first-degree-murders Peter, and doesn't have a confrontation with Harry at all.
I do think Voldemort still comes back though. Trelawney would still have made her prophecy ("His servant has been chained these twelve years. Tonight, before midnight... the servant will break free and set out to rejoin his master.") In this universe, that prophecy would refer to Barty jr, finally throwing off the Imperius curse for the first time.
Bertha Jorkins still goes on her trip to Albania, and... Voldemort probably just possesses her the same way he did Quirrell. I bet that's easier to do after someone's been sort of fried by a memory wipe. Also, being in her head, I have to assume he's eventually gets some inkling of the fact that Barty is still alive, and so goes looking for him. Harry still goes to the Quidditch World Cup since she's friends with Ginny, her scar is still hurting (she probably writes to Lupin about this, instead of Sirius, but Lupin gives her pretty similar advice. He will have still left Hogwarts, because Snape would still have outed him as a werewolf at the end of the year.)
Harry still ends up as Champion. I think Big Sister Fleur would be a little more protective of Fem!Harry than Canon!Harry. And also... Harry just straight-up has a crush on handsome, nice, good at Quidditch Cedric. Rita could write about the Harry/Cedric/Cho love triangle, instead of Harry/Hermione/Krum.
The Yule Ball would actually be kind of a big deal for Fem!Harry. Up until now, she's been kind of a tomboy who wears Dudley's hand-me-downs... and is occasionally forced into some terrible 'party dress' when Aunt Marge visits. Harry's best friends are a boy and a tomboy, her quidditch teammates are feminine role-models but very much athletes: 'girly' hyper-femininity is something she associates with Aunt Petunia.
But, fourth year roles around. Mrs. Weasley buys her a set of emerald-green dress robes that actually look really nice, and she needs to find a date for the ball. I think she thinks about asking Cedric... but chickens out at the last minute, and asks Neville to go with her as a friend. Between her much more girly roommates, and Fleur taking pity on her and giving her some tips... I think Hermione's big Yule Ball glow-up is also Harry's first experience with wanting to look pretty, and succeeding.
I think it would be fun, and make sense, if this lead into a little secret admirer subplot. Someone is leaving her little gifts and messages, and she's thinking - is it Neville? Theo? Cedric?
(it was Draco. Instead of the blast-ended skrewts, Hagrid has them all taking care of Harry's basilisk, and like... she has a basilisk... she's the Heir of Slytherin... she asked Longbottom to the ball when she could do so much better... she was wearing green and looking perfect. Draco's Harry obsession has sorted itself out into a very serious crush.)
Back to the main plot. With Peter dead, I'm not sure Barty would be able to take care of Voldemort AND prep the ritual to bring him back to life AND impersonate Moody. He's going to need a man on the inside. I think at first he tries to use his father - but as we know that is going to get very risky very fast, because Barty Sr is remarkably good at fighting the Imperius curse, and also just knows way too much. He's a huge risk, because if he goes rouge, he'll tell Dumbledore everything (which is very nearly what happens.)
So I think Barty Jr. targets Barty Sr.'s assistant Percy Weasley, after he can no longer control his father. Uses him as a way to affect things in Hogwarts. He might imperius him, but he also might just like... Polyjuice himself into his father for short periods, and manipulate Percy in a non-magical way to make sure he helps Harry, and gets her through the maze to the cup first. Once Percy realizes what he's done... I think he re-commits to his family in penance, and stops being a such a Ministry man.
Voldemort rising works as kind of a reset button, so things would start looking a lot more canon again, only with Ron and Hermione swapped out for Ginny and Neville. Main difference being, Voldemort has Barty now. I absolutely think he would have survived Book 4.
So I'm going to leave this what-if here for now. Thanks for the ask, this was a lot of fun to think about.