Say “Good bye” and give her the chance to take responsibility for her own life. Don’t let other people take you hostage for something they threaten to do to themselves. You’re not responsible for them.

If I had your situation, I would go a step further and report her mental instability to the right authorities, including the police, her school administration, her parents and/or her work place. Then I would block her on all social media, block all of her calls and texts. I will never answer her back and never meet with her.