"Yes, but you have an ethical responsibility to help anyone you have a reasonable belief will be in harm's way, madness-inflicted or otherwise. This feeling of duty will be much more intense if it is your very-recently ex-girlfirend. You know, the girl you just spent three years feeling protective towards?
This would be the source of guilt, at least for me. Not any sense of "oh, crap, I broke her." "
Been there, done that, have the mental scars from dealing with years of BS trying to deal with an unstable individual. IMHO, I'd express any concerns regarding her with her immediate family to give them the heads up on the situation. Then cut all ties and walk away.