Look up Borderline Personality Disorder. See if any of that looks familiar to you.
If it does, you might should know there is no medication for any personality disorder. It isn't a chemical instability, instead it is a problem with how they think, which medication can't regulate. Therapy can help, but only if the person is willing to realize they have a problem, and actively work to correct it, of which many with personality disorders are unwilling/unable to do.
She isn't going to hear you, and the best you can do, is not buy into her guilt trips. Be polite, be respectful, and don't waste your time arguing with her, as it isn't going to change anything, instead, walk away. Reaffirm that you love her, and respect her, and walk away. If needed, tell her you need time to cool off/ whatever, call it a "time out" and walk away, until she calms down and regroups.
By the way, therapy for you, if she refuses to get help for her, can give you an outlet, and techniques for dealing with her.