Hi, sistershelp;
And welcome to SR and the MH forum!
I have no experience to share with BPD.
But, I do have experience with dual diagnoses. My son is a heroin addict and bipolar. He is on again/off again now, and is waiting for a bed in a year long facility now. It's a very difficult thing to deal with, and my heart goes out to you.
Here's some information about BPD from the Mayo Clinic;
Borderline personality disorder - MayoClinic.com
There is hope.
And I can tell you that, if she is being treated for both her substance abuse and her mental health issues together, she has a much better chance for successful rehabilitation. Age, too, helps stabilize those with both conditions.
I uge you to attend alanon or naranon meetings. You will get support in learning how to deal with the addiction side of your sister's problems, and learn how to set valid boundaries. Your neice would benefit from alateen. And you may get some helpful information from our naranon forum here, on SR too. Here's the link:
http://www.soberrecovery.com/forums/...tance-abusers/
I wish you well. Please let us know how things progress.
Shalom!