Friend or Fake

So I have this "friend" that I used to hand out with everyday. we carpooled and told eachother everything. then school let out and she suddenly stopped talking to me. she only called me 3 days after my birthday to first ask when it was and then complain about a boy who she broke up with 3 months ago and a friend who did nothing. I felt used, and offended. she came to my house yesterday for a school thing and the entire time gave me dirty looks. I have done nothing to her. I tried to be supportive even though her break up split up MY friend group. HELP!!!