Petunia knows there is something special - something strange-special - about her sister before Lily does.
It is in the way Lil-lil plays.
Lil-lil is two and a delight. Pet is four, and despite the occasional bout of jealousy, is mostly just reveling in being the Big Sister, which is, Pet thinks, really something special. Lil-lil has bright red hair and bright green eyes and a bright wide smile, and Lil-lil adores her Pet.
Lil-lil also has absolutely no fear of danger, and goes bounding merrily into trouble.
Somehow, Lil-lil never gets hurt.
It is only when Pet, who takes her role as Big Sis seriously, watches her little sis float down off the counter, light as a dandelion puff, that Pet really realizes Lil-lil should have gotten hurt.
Lily never remembers the incident, and Petunia puts it out of her mind like a bad dream, but it is the first time Petunia sees Lily's magic and it is the first time Petunia cries over it.
It is not shock that makes her cry, but rather fear.
They are eight and ten respectively when they have the misfortune of meeting Severus Snape.
Lily, as usual, is being an utter brat. She always is, when Mummy's not there to watch them, when there are no adults around to play goody-two-shoes for. Lily's magic - that is the only word Petunia can find that fits Lily's strangeness - means that Lily never does get hurt, even when she does wrong things, like jumping off the swings or out of trees. Mummy always tells them not to, but Lily never listens. She never feels the need to.
It doesn't help that Lily is utterly enamored of herself. She gets more and more enthralled by her own strangeness, her own magic, by the day, and takes to doing more and more unnatural things, even - especially - when alone with Petunia.
Lily knows Petunia hates the way Lily can make the world dance unnatural steps to her tune.
"How do you do it?" Petunia asks that day, startled at the note of wistfulness in her own voice.
"It's obvious, isn't it?" says the freaky Snape boy, who Petunia later realizes was stalking Lily the whole time.
He lords his knowledge of the "wizarding world" over them, buttering up Lily in his socially-inept way and tearing Petunia, who is only a muggle after all, down into the mud.
Lily puts on a good show of glaring at Snape when Petunia, after a few brittle laughs, drags her off, but Petunia is not fooled.
When they get back home, Petunia storms past her startled father up to her room, throws herself on her bed, and cries bitter tears, because Lily has never been able to resist the siren call of magic, and a sister doesn't hold a candle to that.
The wistfulness earlier wasn't a longing for magic, but a longing for it to go away.
Petunia doesn't want to go with her sister to the platform. Lily is eleven, bright, confident, and as sweet as arsenic-laced sugar.
Petunia is thirteen and despises her.
Lily is the special one. Lily is the pretty one, and isn't it just sad how plain and even horsey Petunia has turned out? Lily is the nice one; Petunia is just a shrew and a nag. Lily is the smart one, Petunia never quite as bright, despite their grades being more or less par. Lily is the one with magic, and oh how tickled their parents were when the letter came.
In a fit of desperation, Petunia writes to this Dumbledore, begging him to take her. She doesn't care that she can't do magic; she can at least sit in and learn the theory. Surely there is some place in the world for a normal girl who understood magic. Petunia might not be Lily-bright and Lily-perfect, then, but she would still be something special, something worth noticing.
But the Headmaster sends her a condescending little note informing Petunia that while he "understands her desire to be close to her sister," she is just a muggle, and oh, Petunia hates that word with a passion. She knows a slur when she hears one.
The Headmaster of Hogwarts is an incredibly stupid man, Petunia realizes.
It figures that Lily would have read her mail. In their parents' eyes, their teachers' eyes, their neighbors' eyes, Lily can do no wrong, and so Lily does nothing right.
Tears clouded her eyes while she wrote the damnable letter, but when Petunia drives her sister away from her on the Hogwarts platform, her eyes are bone dry.
Something vital blows out of the Evans household after that. Petunia swallows a lump in her throat as she goes about her day-to-day, humdrum, muggle life, as her parents do, her parents separated from her as by a vast gulf.
A gulf named Lily.
They talk of her incessantly. How proud they are of her, how wonderful it is to have a daughter at such a prestigious institution, how she will make them all proud for years to come. Lily writes them religiously, and they cling to her every word.
Petunia doesn't even dignify the letters Lily sends her with a burning. She just shuffles them in with the junk mail and tosses them away. After a few months, Lily finally stops sending them to her.
Holidays are the worst, though Petunia's not sure if Christmas or summer is worse. Summer means months stuck with Lily and - for the first few years, anyway - Snape lurking about, and putting up with visits from all of Lily's nasty friends, quick to perform "harmless pranks" on Lily's boring, skittish, muggle sister, and any complaint from Petunia is met with pitying eyes from her parents, brassy laughter from Lily's clique, and admonitions from them all for Petunia to "get a sense of humor, already".
But Christmas is family time, and Lily is no longer family to Petunia. Having her there, welcome at the table like an equal, like she still lived there, like she still had any claim to their home, is like a spear to the side.
At least Lily respects their parents' wishes enough to not drag her friends over for that break.
Lily comes home less and less frequently, until by her last two years, she doesn't come home at all. It breaks their parents' hearts, but Petunia's heart has long been ground into dust.
She has learned not to cry when Lily is around, but Petunia cries every night when she's alone again, and it has nothing at all to do with Lily, except that it is all about her.
By the time Lily gets married, Petunia has been married for a year, and their parents have been dead for a month, killed by wizarding fanatics who are too cowardly to kill the one they really want dead.
Petunia rips up the invitation and gives it back to the owl that brought it to her. It dutifully flies off, back to her witch of a sister.
(In fairy tales, witches steal human children and take their souls, and Petunia finally gets those tales like she never has before.)
(The wizarding world is a vampire. It steals the best and the brightest from those who love them, sucks them up and never lets them go, and drains the life right out of those it tramples in the process. It rips the hearts right out of those left behind, takes and takes and takes until you have nothing left to give, and takes some more, all because it can and you are not special, pet, not a witch or a wizard or lit and lifted by any fiery spark of magic. You are just mortal clay, lifeless and useless, golems for its amusement, and it winds you up and watches you shatter.)
(Life is hard enough, without the unthinking cruelty that is the lifeblood of wizards.)
(Better a monster than a victim.)
Three years later, they don't even bother to send her a proper death notice, or tell her in person, or anything like that.
Why should they? Petunia thinks, staring down with brittle-hard eyes at the letter in her hands. She is, after all, just a muggle.
Petunia methodically shreds the pretty little parchment with its pretty swooping calligraphy into the smallest pieces she can, then throws them like unfortunate confetti out into her yard.
She picks up her nephew that she has never seen before, dumps him unceremoniously in the hallway, then goes upstairs and screams.
Vernon comes running and finds her on her knees in their bedroom, sobbing her heart out and chanting a name she refuses to speak.
Everything dissolves away in water. Even blood.