Whats that stalker movie with that creepy girl?

Like ok so there is this girl who is perfect and the other girl isn't pretty or anything and like the pretty girl starts like helping the girl out and the imperfect girl becomes obsessed with the perfect girl doing the SAME thing she does and then the perfect girl is like freaked and in the end the imperfect girl tries to kill the perfect girl and then gets arrested. I neeeeeed to know what its called haha i think its something like roommate i don't know thank you so much.