hi Newy and

I can only imagine what I was like trying to deal with the daily-ness of your daughter's needs along with a separation. Pretty intense i'd imagine!
And I understand what you're saying about the "steep learning curve"... .I know when my T (therapist) suggested I read the book "Stop Walking on Eggshells" by Randi Kreger after i'd been telling her things that had been happening with my H (husband) that I couldn't understand, I was amazed to see how much of my life was in there! But I was surprised how much it helped me to know what was the motivation behind his actions, and be able to begin to relate differently and communicate differently without setting off every trigger he had.
By the way, Randi Kreger has a newer book out about BPD:
Essential Family Guide that's even better, since it includes information she's learned between the last book and this. i'm reading it now and it's very well laid out and easy to read.
Honestly, I think there are various theories about what causes BPD (nature vs nurture and all that,) but even though I like learning all that background info too the best and most helpful things have been the insights to their way of thinking and then the tools we can learn to stop the circular arguments, how to have a conversation without triggering an onslaught of emotion, that sort of thing. Here's a great article on
Family Guidelines to help a parent know where to start with boundaries etc.
This is a good discussion on your question of what's behind BPD, and Randi Kreger, the author of the books I mentioned above, weighs in on the conversation with some great stuff:
What is the cause of Borderline Personality Disorder?i'm so glad you've found the BPD family community! It's been a huge help for me in the search for solutions to the problems that come along with BPD loved ones. Welcome to the learning journey!