Hmm. This may sound cold:
You’ll undoubtedly be on the receiving end of this – if you haven’t already – possibly many times. My guess is its even more likely you will be if she’s just wiped out her last friendship. You might well be cleaning up behind her for the rest of your life. Then again, she might stop pissing people off from this point forward. The reality is probably somewhere in between. You’ll definitely need to help though, maybe for a very long time. She may need counselling, different meds, who knows what.
I can’t honestly say I would stay, in your shoes. For me it would probably be rather critical to know whether she knew, admitted, and was genuinely sorry about being a dick to people as a general ongoing thing, and wanted to change in order to stop ballsing up your lives, plural.