It is hard to work in a strained environment. I am sorry that she is creating so much havoc. Would it be beneficial for all of you to talk to her together and if that doesn't work then the director of your department? Of course there are repercussions to any of your actions but you sound very unhappy the way it is now. Good luck it is always hard to deal with people problems. There are regulations about having to work in a hostile environment. A strong stance but it is an option.