I don't know much about this...but I can tell you a few things...
It is often thought of as being caused by early childhood trauma. However, recent thought is that it might be caused by neurological issues.
Borderline (BPD) is considered a difficult to treat diagnosis and difficult to live with- one as well.
Some mental health professionals have mixed feelings working with a patient who has this diagnosis.
However, it is VERY important that someone with- the diagnosis receive very good therapy. Therefore, it is probably wise to find a therapist who has experience in this area and is comfortable with it.
Some say medications don't really help...others feel strongly that medications like antidepressants help significantly.
Many parents really like a book called "Walking on Eggshells" (might not be the exact title...but it is very very close).
Ironically, I JUST bought the book myself and got it probably yesterday. My very close friend has a daughter with- this diagnosis and additionally, I thought it would help me with- my studies.
As a side note...prozac has been helpful for her daughter...but she only takes it on and off...it's been very very difficult for all of them.
Taking a very quick peek in the book last night, I noticed that it is important to understand where these kids are coming from, maintain boundaries, try not to take things personally, provide treatment for patients (esp. if they are open to it) and to get support for yourself if you feel stressed (which is often the case).
The authors mentioned that remissions is thought of to be very difficult with- this disorder, but that if the patient is open to treatment and works hard at it...it certainly is possible and success has been enjoyed by many.
Sending you good thoughts...well wishes for strength and wisdom.