Thank you all for your helpful input.
It's funny but I've run through these things you've written in my head. Not to serve as a crap dump truck. Not to enable by just sitting there and listening without reflecting. That if she's staying with him, she should stop bitching about him so much. And also that I love her and maybe by quietly bearing witness that is all I should and can do. And last that boundaries should be adjustable --- and I think I may have to adjust mine.
This woman is a person whom I think so highly of. Part of it just frosts me so --- she's drop dead gorgeous, funny, smart, kind and successful and any man would pretty much die to have her, and she puts up with a narcissistic turd who doesn't even like or respect her.
I am SO glad I gave my AH the boot! So glad!