This has probably been done before and better but Consider: Petunia was the witch and Lily was not.
Okay, so instead of being a bitter jealous hurt person Petunia is a happy one. Lily is excited beyond the telling of it. She has to know everything. Petunia likes the attention too, likes being cool. They stay close. More importantly for the first time in her life Petunia isn’t an upper middle class kid, she’s a Muggleborn. She can never be a Pureblood. This totally refocuses how she sees people. Hell, even Lily’s stupid little friend from across town in his patchy hand-me-down clothes is a Halfblood and that’s more than she can say for herself.
Okay, Petunia gets furious when Severus has the unmitigated gall to keep talking to Lily over breaks like they’re still friends. She knows the kinds of people he hangs out with and the racist bullshit they pull. How would they feel about his little Muggle friend, hmm? So imagine our girl Tuney in her Ravenclaw robes sidling up to the Slytherin table at lunch and asking after Sev’s mum. Mentioning low key that he and her little sister (no magic, poor thing), are best friends. Imagine her casually dropping his soppy letters home to Lily that she stole so there is no question he’s a garbage little liar.
But also Lily. Lily is at the center of all of this. Lily. Learns. Potions. Petunia doesn’t teach her, it doesn’t even occur to her that Lily can learn. No, this is all Lily’s doing, Lily whose sister comes home on holiday her pockets full of frog spawn turning teacups into rats, Lily who wants to play too, just straight up breaking into Tuney’s room while she’s out. Lily who practiced basic spells with her sister’s wand and refused to cry when she noticed they were never, not in a million years, going to work. Lily who didn’t quit because of that, who read the History of Magic textbooks because even magic history is just history until she could ace the HOM O.W.Ls. Lily who, and this is canon, saw potions and it just clicked. There wasn’t any hesitation or doubt, she read the textbooks and it all came together, the timing and the nature of ingredients and the precision. It’s not too terribly much different than baking and Lily is so good at that her mum thinks she ought to pursue culinary though Lily reckons she’d rather focus on chemistry. Petunia finds out when she catches one of her essays corrected in red pen instead of Slughorn’s sloppy quill work. “He was wrong,” Lily explains, not remotely apologetic, “I mean you were wrong too, but he was wrong about why you were wrong.”
James still loves Lily. They meet at the train station when she’s seeing her sister off. “Are you going to Hogwarts?” James asks. Lily smiles, but sadly, “Not this year.”
Just before that happened: “I’m sorry, I’m sorry you can’t go. I’m sorry. I thought when you turned eleven you could go too but…. but it’s not like that. There’s nothing I can do.”
“Don’t be silly, Tuney. I’ve got Mr. Feathers, I’ll write this Professor Dumbledore and persuade him to change his mind!” (Petunia’s owl is named Mr. Feathers as creativity is not her strong suit)
Anyway, no, James still loves Lily and he is still every ounce as stupid about it. She’s the girl from the train he always just misses after that first time. Is she a Prewett or a Weasley, maybe? With that hair she could be either. Maybe she’s a squib. There is something about her that bothers him in an ‘I want to pull her pigtails’ kind of way. Never in a million years would he associate the Little Red-Haired Girl with, of all people, Petunia Evans. Who would?
So, okay, yeah, Lily is stubborn and Gryffindor af. Personal letters get owled to Dumbledore on the daily insisting she be permitted to attend her sister’s Quidditch games as it is only fair. (Petunia doesn’t play, she’s the announcer)but Dumbledore is still himself. He’s positively charmed by the angry little Muggle girl writing him because he loves moxie and also chaos. Besides which Lily learns he likes lemon drops and mails them to him as a bribe. Which, yes, this really messes up James Potter on a deep personal level because here is this boy, trying to play Quidditch and just avoid all the random conspiracies that infect his life and then in the MIDDLE OF A GAME James flies side by side with Sirius, quaffle in hand, “Si, hey! Hey! Look over there, in the Ravenclaw section! It’s the girl from the train station!”
“ARE YOU MAD??? GO THROW THE BALL AT THE HOOP YOU DAFT BASTARD!”
“Who is she?”
Sirius, at this point, hits a bludger at James on purpose.
“I saw stars when I looked at her.”
“You saw stars because of a head injury I gave you.”
“Yeah, what the hell, mate?”
Somehow, I’m not sure how, Petunia gets into the Slug Club. She brings Lily to a party as her +1. Slughorn is amused but not annoyed, like, “Ms. Evans, when you said you were bringing a guest this was not exactly what I expected and you have never been one to do the unexpected.” But Petunia does not back down. “Professor Slughorn, it’s just a party. Though, if you get a moment then I think you’ll find that my sister is exceptional at potions. And I don’t mean for a Muggle. She’s probably at a seventh year level, though I’m not a potions professor so what would I know?”
“A great deal, I would imagine, Ms. Evans. If your judgment has failed you I’ll be terribly disappointed.”
Again, I want to make it very clear, in canon, Lily was in the Slug Club because she kicked ass at potions. This is different. Here Potions is the only magic she has, the only connection to her sister’s wonderful world that she’s able to touch herself. She’s better than witch!Lily ever was. Horace Slughorn is so delighted he makes her a member. After some tipsy bickering with the rest of the staff Lily is afterwards invited to all Slug Club functions. She floos in, always with ashes in her hair and a fire in her heart.
It gives her a nickname, the way she comes to the parties. She’s called ‘Fire Lily’. Every time she arrives it’s by flame, she smells of smoke and her hair looks like embers. James is the one who starts it and, after hating it for a few months, she loves it. Magic has given her a new name. She belongs there. No one could ever argue. She doesn’t have a house or a wand or any magic of her own but she belongs there because she and Petunia insisted she belonged.
You can’t just have someone as pig stubborn and smart as Lily Evans with her opinions and determination and expect she has anything other than absolute willingness to throw down against some Pureblood elitist that calls her out. Without a second of hesitation Lily Evans agrees to duel some racist brat that decided to be a crybaby about her magical status. Literally everyone tries to talk her out of except James who has stars in his eyes and Petunia who is just like, “No, she does this. She’s doing this. I can’t keep her out so she’s going to embarrass me horribly but trying to stop her would be worse.”
The duel happens. It’s tense. People have gathered to watch. Lily Evans is holding a wand that someone loaned her. The second the match starts she pitches the useless wood stick at the face of the idiot who ever thought fighting her was anything even approaching a good idea. Without an instant of hesitation she bum rushes her opponent and tackles them, a nasty hex grazing her in the process. Still, by the end, neither of them has a wand and people have to drag her away while she’s still throwing punches and kicks and trying to bite.
Later, in the hospital wing, “Hey, Tuney, I won a duel.”
“I don’t think we can convince the headmaster to let you try the sorting hat but there’s not really a point. You’re a Gryffindor.”
