I see your way of thinking here, but it's not entirely possible that she started to like him. After she caught him peeping she obviously wanted to get her revenge, but probably didn't thought she'd fall for him. After all she said she liked how he stared at her. She was probably tired of her previous life, and Emile Hirsch's character is certainly not bad on the eye. Even if there's a slight chance I don't see why it's not possible.

It's not hard to love a character who is designed to be attracted to you for being you, and nothing more. The girl basically exists only to make the main character a better person, and seems to attach herself pretty hard to a kid who she caught peeping on her getting changed.
I think you should ask yourself if you really know anything about her character by the end of the movie. You'll be surprised how little you can come up with.
I'm not complaining, I still like the movie and have watched it numerous times. But I just think it's fair to call it out for what it is.

*mistake on the last line - I wasn't asking a question lol .. Ignore the question marks