Mean Girls problem?

[751]

I study in a small private school, and im my grade there are just 9 girls, including me.
1 of them has super-religious family. They dont allowd her to go to the mall, someone's house, invite people to her house, etc.
2 of them dont have personallity, they copy everything
5 of them were cool but them they converted into mean girls.
I decied to stay away from everyone and im okay in this way, i eat with my best friend (whos a guy) his friends and my guy friends from other grades i dont feel bad or nothing.
The thing that was bother me was the thing that 1 of the girls talk really bad about me, saying that im a b with an ich and that im fat and i dont have friends and stuff like that. i know that noone of those things affect me, anyway.
But yesterday the girl sent me a :* thought her friend's facebook, i just answered with a boring smiley-face
and today i post a pic in instagram and this girl put something like i love your hair.
I know that she hates me, and she hates my best friend too.
What should i do?