As I said, my adult daughter has BPD. She was born different. She was a fussy, distant baby, a hard-to-raise child, and once adolescence hit, it became a nightmare of bulimia, self harm, substance abuse, hospitalizations and halfway houses.
Therapy and meds didn't help much, if at all. Finally she found a partner who was even more messed up than her, and they "found Jesus" together, eventually got off drugs, got married, and started popping out kids. I do credit her church for some of her success in getting off drugs. Apparently the black-and-white rules of an evangelical church help. Also, it helps her to volunteer and be a part of a community, sing, socialize with others who have struggled with drugs and gotten clean, etc.
Still, I don't have contact with her except a phone call 2 or 3 times a year, her choice, because I am not Christian (!). My older daughter says the husband abuses the children. (My older daughter HATES her brother in law.) My BPD daughter has had a kid every other year for 10 years, and just announced her 6th pregnancy. My heart breaks for my grandchildren (whom I am no longer allowed to see!). Soon they will start hitting adolescence, and I hope for the best, but expect the worst.
(I always worry about the children. I worry for yours. I guess it's good they're not around her much.)
At the same time, along the way, my daughter got some education and got a career as a phlebotomist. She no longer self harms (as far as I know), but she gets paid for drawing blood. Maybe that helps.
(She's not all bad. She's intelligent, she's very caring, she has a sense of humor, she's friendly, she's highly energetic and gets stuff done. She's just full of anxiety all the time.)
Anyway, back when she was a teen, I read the book, new at the time, called Stop Walking on Eggshells. It is written by people who themselves have BPD who have it pretty well managed. It's a book for loved ones of those with BPD. It has helped me understand her condition and draw boundaries. Maybe you've read it, Jezeera.