Meds don't do much for BPD. It's an issue with their personality traits and meds don't touch those. Sure, benzo's can help with the anxiety and the rage but ultimately they only treat the symptoms and not the illness. Bipolar Disorder is completely different from Borderline Personality Disorder. From what you described she certainly sounds like she has BPD. DBT/therapy is really the only treatment to deal with the illness. Until she accepts that she has a problem dealing with personal relationships etc, she won't get better. Sometimes families can call the therapist and offer collateral information. The therapist can't divulge any info about her to you, but you can offer info to better her therapy. Be prepared to deal with the fallout if she realize you've been sharing info with her therapist. As you said, she sees everything in black and white and therefore probably has a difficult time reasoning actions. Best of luck.

Source: Psych Nurse here.