You are absolutely right. She can pick up on my emotions before I can sometimes. What you said makes perfect sense. Lately I feel like I can't relax. I know that at any moment she can get upset at me and I will have to go through it all over again. How do you do it?
For me personally, I focus on what I can control. I can work hard. I can clean up the house and take care of the dogs. I can treat my ex-wife or daughter (both BPD) kindly, even when they're not kind to me.
In an argument, I can't make them see my point of view when they're unstable, but I can calm them down and get rid of 90% of the drama. That gets rid of the worst of what we experience- simply don't fight. Focus on her emotions and calming her down, and if that fails then tell her you're going for a walk so you both can take a breath.
Or take an alternate route- just actively listen and when she finishes ranting, respond with, "I'm so sorry you're upset, what can we do to make things better?" Maybe she rants away about how this is all your fault some more. Stay calm, actively listen, and repeat a similar phrase- apologize for her emotions (not what she's accusing you of) and then ask how to help.
When you're walking on eggshells, they're ALWAYS going to break. It's inevitable. So stop walking on eggshells. Stop anticipating chaos....because that brings the chaos!