I had this problem, too, some (2-4) years ago. I know it's not that easy but you gotta ignore her. She'll try not to show it but she'll be damn angry. For me it was a help to find people who had the same problem with this girl. YOu get better ideas and moral help together. Talking to teachers can put her down a little and can cause that she failes a lot of tests.
My last problems with her were solved when people grew up and didn't celebrate her for what she was doing anymore. Well, now she isn't at school anymore and the atmosphere there is much better now. I hope you can find a solution. But I'm sure you will. This girl acts like a child and anytime she gotta realize that she isn't one anymore.