How do we deal with a horrible co-worker (details)?

I work (closely) with a woman who is bitter, jaded, and just generally unhappy with life in general. (I base this on some things she's told me personally and some things other co-workers and I have witnessed.) She has something nasty to say about just about everyone in the office, but she's nice to these people's faces. Nobody really likes her because she's very haughty and has this "holier-than-thou" attitude, and is a major kisser. People in the office generally don't like her, but nobody will speak up to her. We're not really sure why, other than she works for one of the named partners of this firm (law firm). I was hired on to work for this same attorney (he's very busy, lol) and I have to work very closely with her. I'm tired of her childish, hateful comments about people and really want to find a good way to tell her, once and for all, to shut the hell up, I'm tired of your hateful, immature BS. I can't say anything this unkind though, and risk losing my job. cont...