People who are potentially dangerous are at their most dangerous when being rejected. If you had to fire someone like this, how would you go about it?

I guess I should point out that I am not the manager in an office nor am I boss of a company. I am a onetime/sometime film writer (mostly unsuccessful) and she is my long time literary representative for one film script she us pushing. She is part of a sort of film studio mafia, an old cult-like group. She has made some serious threats a couple of years ago. But I don't want to live in fear. I have given her a quiet but clear ultimatum; the threats and bullying have to stop. Obviously, there is a long, complicated story here. Some of it goes back to my past (as a child in a world dominated by this cult-like group). She was very humble and sweet in our last conversation...but I know her and I am waiting for the other shoe to drop.