im a girl, with a girlfriend. whos my best mate. i dumped her, but realised that the only way to keep her as a mate, and my other best mate (a guy i am sharing my girlfriend with, this may sound weird ...
Before you dump her, or anyone else with such deep mental issues, is to help her get the therapy she needs. At least you will feel that you helped another suffering human being and she might listen to your advice because you were all once good friends. Then dump her if you still want to.