Whether she goes further down the toilet doesn't have anything to do with whether you cut her off.
Personally, I just wouldn't accept angry, abusive or irrational phone calls. You don't have to engage with her to do this. You just don't answer or you change your number or you delete the message when you see it's from her.
I'm sorry you are in this situation with her. If you will read the sticky posts at the top of teh F&F page, you can gain a lot of insight.