Time to break up with my last friend?

I have one friend left. She has problems. She started calling me during the pandemic. But after a little while of this I stopped answering.. she downright lost her mind and called like 50 times in a night so I figured I should probably just talk to her. I assumed when I went back to work she would stop. But she hasn't. Now I am hoping when she goes back she will stop.

I have accepted my role as listening to her even if I think a lot of what she says is wrong. And if I am not interested in something I hear I just brush it off.

But last night, she did it, she pushed me over the edge... I told her one thing, one thing that means a lot to me and she meanly dismissed it like I was nerotic. Sort of insulting me in the process. The issue is, it is clear now, I am not supposed to talk, and if i try to, it will be met with rudeness. This happens a lot with friends- at first, when they are on their best behavior they listen... when they start taking you for granted they don't want to hear anything you want to talk about.

I have always had a "switch" with friends and when they push me too far, I drop them... my switch has been activated. I can't just drop her for a lot of reasons...
1. She is a trusted co worker who I sometimes need for help.
2. She knows every last nasty thing I have ever said.
3. She the last person in the area I could call if I was dead.

She has a history of this. She used to have a best friend where she worked who she tells me now has stopped talking to her. One reason I tried to be there for her. But I think what happens is she calls all the time and complains about her troubles... but really 99% of her troubles are her own fault and you can't really offer her any help because she doesn't want it.

One recent thing is that she got a review that was only good, not excellent. I got excellent. She is upset about this but I can't see why from a purely logic point of view. Both of us have been there so long we can't get raises. So it really makes no difference. She says it makes a difference if she wants to apply for another job but she did get an excellent last year so it isn't as if she would have a hard time moving on. She is angry that they are going to give her a new job -- which will mean a *slight* reduction in pay. (but I worked it out and after taxes in a lower tax bracket she will be about the wage I a have) I do get that. But the new job will be so much less work... I told her I am jealous. She has this job, to be fair, because of her behavior. Her prior behavior got her fired. We both had bad bosses but during her time, she was written up by one, and got fired by another. Even though I had a bad boss... worse than hers.. I never was written up and all my reviews were excellent. So yes, it makes sense that management is going to treat me slightly better.

She is just not being honest about herself. I am willing to be supportive but it is starting to launch into illogical thinking and she is so consumed with her perceived slights, you better not talk about what is going on with you!

At this point I think I do have to nicely tell her to stop calling so much. I have to go back to work next week for 3 weeks, one of the longest time periods. I am going to tell her that because I can't really talk on the train, (pre pandemic they had a quiet car -- I will tell her that has gone back into effect) she shouldn't call.

I just wish I knew why this always happens. After someone talks to me for a while they just lose all respect for me.