Welcome Kygirl49:
Sorry to hear of the problems with your step daughter. They generally wait until age 18 to give a BPD diagnosis. You don't need to wait for a diagnosis to start using strategist skills and communication techniques.
The Tools listed in the margin to the right can make a difference. Check them out one at a time and give them a try.
What are some of her most disturbing behaviors? Has she learned any coping skills and self soothing techniques from her counselor?