Why is my friend bitching about me?

my so called best friend... talk ill about me to anyone . her colleques, her family members, he friends, even to the people who knows me well.i never knew this, only 2 months ago that I know.so all these while I trusted her.
when ever I tell her about my problems with my mother, my brother or a small silly thing, she would tell others about it with spices of words. and if I tell her I meet a male friend she would tell others that am too desperate of a male companion, or I am too excited to talk only about boys, she even call me ugly and no males did really like me. when I drive too she would ask to drive my car for I cannot drive well like hers... she tell others I am a sick in the mind person...
why is she like this... is it ok for me to proceed with her friendship?... I am so hurt when I know this and it really surprises me for this woman I put up as my mentor do this to me... and now I heard it with my own ears that she talk ill of me for my very own co-workers recorded her talk.what I do? help

Is she your best friend or your worst enemy? Some people are just born to gossip. The only answer for dealing with someone like that is just don't give her anything to talk about.