Hi and welcome to the board though I am sorry for what brings you here. It is good that you re reaching out for help and support here.
Who suggested she has BPD? Has she ever been in therapy or seen for behavioral issues? What you describe certainly sounds difficult. What sort of drugs and self harm does she do?
We have several articles, one of which I am linking here given your question:
I think it's Borderline Personality Disorder, but how can I know? You question is one we get here a lot but unfortunately none of us can answer it. What we can do is listen, support and help you find different ways to approach your step-daughter. Sometimes making changes in us can help them. Mostly though, making chances in us helps us to cope better as it is very difficult to live with a person with BPD traits and disordered behaviors as you describe.
I hope we hear more from you as you settle in. I also hope you jump into other threads and post as that will help everyone including you.
