At some point, between Petunia's periods of hatred, there had been a week or so when the both had fantasized. Small children, eleven & twelve, dreaming about Hogwarts. Lily had already gotten her letter, and they hoped that maybe, it wasn't too late for Petunia.

Lily would have an owl, Petunia a cat. Lily's wand would be long and light, while Petunia's would be sturdy and darker. They would both ace their classes, though Lily liked the sound of Transfiguration and Petunia liked Potions more.

They would both be in Gryffindor, since Severus said it was where Dumbledore had gone and Petunia wanted to be with Lily. They would ride the train and try all sorts of candy. Severus said not to eat the every-flavor jellybeans so Petunia would definitely have them. Lily wanted to try chocolate frogs- she was brave like that. Petunia shuddered at the thought. Frogs in your mouth!

Of course, they'd both be super popular and win the House Cup for Gryffindor. They were sisters, and they would always stick together, even if they fought.

...

It was not to be, of course. So Petunia went back to hating Lily and her perfect life, and they went their separate ways.