How do I work with someone who I know is talking about me behind my back?

This person I thought was a really good friend of mine has been talking down about me to the other co-workers at work. I know she is doing it to make me look bad and her look good. Whats worse is things I told her in confidence are being twisted and told to others as well. And yes! It gets worse. This supposed friend is the right hand person to the boss and i have seen first hand what the 2 of them have done to others and all of it.....based on lies! LIES to make herself look better. I don't understand how someone can be so cruel to ppl that work really hard and do their job while she is busy chumming up to the boss. It isn't right not even close. I don't give a crap if she wants to be a brown noser, I could care less. I just don't understand why she would do this to me and still try to act like my friend. How do you deal with that knowing that even if I do confront her she will twist my words and probably start something else. I'm so hurt and sadden that ppl still act like this I would never do what she has done to me and some many others. Help! I don't know how to deal with all this and get through my day knowing that she hurt me.