I've not looked at the lessons here. I've read the walking on eggshells book. And I try. But it's so hard to avoid a trigger. I know I'm doing it but can't stop. I think I'm more at the leaving stage - ignorance caused the thread to go in the wrong place. Having said that, I haven't said I want to leave, but we are arguing about the relationship just now. Suicide threats - I do all the wrong things. Panic. Try to help. Let her back in etc. I know it.
Well, it's a good time to learn and get lots of practice. When I first started on the lessons it seemed like I got lots of opportunity to practice them as we had something going on frequently. Eggshells book is good, but the Lessons will really help you remove your part of the dance and increase your odds of having normallish conversations more often.
Validation can really help keep conversations from going to crazy places. I would start there.
Boundaries can help protect you when things do start to get out of hand.
What do you think would happen if you told her you would call 911 if she threatens suicide, and then actually followed through and did it?
When she is really dysregulated, what would happen if you had a boundary set up that you would not take part in those kind of conversations and that you would not leave her permenently, but you would leave the room if it happens?