Are people really surprised that the person who, in chapter 1, fantasized about brutally murdering her bullies and when she finally had the opportunity to do so, did it with a big smile on her face, is not well adjusted by any means?
I like that she actually just instantly falls in love with the pretty girl who acted nice towards her. It's refreshing and more believable than the typical, "Why is this person so nice to me? It's annoying and I just want to be a moody loner" act.
I also like yanderes in fiction, so this seems like it should be fun.