Why are you friends with her?". I would defend her, saying "You guys just don't know her very well... she's not always like that." Until I saw for myself last fall just how nasty she really was. She treated me like crap when I went out of my way to make her birthday special for her, and from that day I vowed to never make excuses for her again, and to stay as far away from her as possible.
It wasn't a forceful removal, in that I declared my desire to no longer have contact with her, but it was a slow and gradual adjustment. I never really told her how I felt about her, because I don't like to cause drama. We just stopped talking. I went from having one best friend to having none in a matter of weeks. The texts and phone calls dwindled, the friendly chatting at work stopped and became all business, and hanging out ceased. My attitude and outlook on life have improved so much since I removed her negative influence from the picture. I am happier.