Hmm, a lot of girls in my grade do that do with each other. If it's at school, I would tell a teacher, but if at home, tell your parent. You could try to ingore her as well, as that will usally work, but like you said in the comment below, she could be tired/grumpy or upset about something, and taking it out on you. Maybe ask her if something happened or if you mabe (i'm not accusing you at all for anything) did something that upset her. And like you said below, if she is making you feel bad about yourself, bring that up with her and tell her how you feel about what she is doing and how it is making you feel. And, also, sometimes friendships just need a little break. This happened once with my friend a coulpe of years ago, and after a little while, we were friends again. Make sure not to stress out about this too much though.
Hope this could help! :)