Are you afraid that she will vent to someone else about you, because you've terminated the "friendship"?

She sounds like the type who will just move on to her next victim. In my last job, I sat opposite two girls who spent most of their time gossiping, only for it to continue on the phone every evening. I call them girls because despite both being married with children, that's just how they behaved. The one was also dangerous.

Yes, there are tactful ways to deal with her. Go through the stages rather than just cut her off immediately. If that's not working, it's up to you whether you want to incur wrath from her or continue to be tied to this arrangement. She's not interested in you, you're just someone to vent to