Why do you think she ditched me and our friends?

So I've known this girl forever and we are BFFs, well we were. It started in December, when she started carpooling with the popular girls in her neighborhood. These girls were really mean to her before, telling the guys she liked that she liked them, making fun of her clothes in front of her, talking about her behind her back. At first, she didn't want to carpool, but then they started getting those frappacinos at Starbucks and she became really b****y and annoying and now she doesn't even talk to me. Meanwhile when we were best friends I never did any of that stuff! Now the only thing that hasn't changed is her awesome gossip, not that I get to hear it besides sleepovers! why did she do it?