My friend is ignoring me?

So here's the deal...

I hang around in a group of about 4 people, I love all of them. For some reason I was closer to Jazz. I have been getting closer to the others and I know that she doesn't really like them and it's like she wants me all to herself. One day, she ignores me for a bit. The next day, she ignored me completely. Not talking, she walked off and stuck with Aimee. I had the guts to ask her if I had done anything wrong and ask if she was OK and everything, I just got simple answers. I asked if it was the other members of the group and she said yeah. After school, I messaged her saying of it was them why was she ignoring me etc. She hasn't apologised to me and I just feel like I've seen a different side to her and I really don't like it. I don't know what to do now.