Be super professional, don't sink to her level, don't acknowledge her influence over other people and don't confront her unless it is unavoidable - e.g.outright rudeness or refusing to do what was asked. I would say that if there was a confrontation , it would force other people to take sides whereas if you concentrate on your own professional approach to her you have the moral high ground. That is what i used to do , but an old friend of mine used to call it "taking the line of least resistance". I never saw it as that myself but i knew i was no good in a fight. It could also smack of being passive aggressive - but what the heck, in the long run it worked for me.