Friends advice please? What should i do?

Ok so this girl on my floor and i were really good friends at the beginning of our freshman year at college. The one thing i did notice was that she was extremely fake not only does she wear 20,000 loads of make up but she one of those people who wants to be friends with everyone and anyone so that everyone likes her and she prides herself on knowing a lot of the freshman cl ect..that didnt bother me but what did was when she would change herself 120 percent when she was around different people, she became so agreeable she lost all of her own opinions. The thing is now..its 3 quarter and up until know we were fine but we had a cl together and one day she started putting me down and ditching me for another girl in the cl. I think she got jealous when me and one of the other girls in the cl started chatting in cl and the other girl was more interested in getting to know me. So shes been really weird and moody lately im cl she wont even acknowledge me (she even turns her back towards me when im standing next to her) and when we are in the same group she does anything to put me down, like im stupid but most of the time i check with the teacher and she says I m right. Like today i saw her in the store and she was like "oh i want caramel ice cream" and she picked one up and i was like "oh here this one isnt no sugar" and she was like "oh silly thats not caramel ice cream!" And looked at it and it said carmel on it in English and in Spanish cause she speaks both languages. And after i left her i saw her get the one i pointed out for her! And the worst is i was with her watching tv and she says "your going to fail that midterm tomorrow" and tells everyone that "she didn't go to class yesterday she skipped" but i didnt skip and i told her i was sick "oh and she didn't turn in her homework yet" why is she telling everyone my business. And when i left to go study she was still in the tv room painting her nails. We still have class together and sit next to each other plus after each class we go to lunch together. Im at the point where i dont even really want to distance myself.