Its a bluff. Ya know what you do? Tell her she is a fucking moron and slap some reality into her. Thats what I did with my friend when she was acting like this. Got her to quit doing all the shit she was doing and even though she said she would just go kill herself. I asked her what that would solve and that she was a coward. Just be an asshole to her without really being an asshole.
Or you could just tell her how you feel and stop being a coward... Either way.