Hi JCSMSMom,
I'm so sorry for your daughter's downward spiral. It had to be awful (mixed with relief?) that she was hospitalized.
Did anyone at the hospital recommend Blaise Aguirre's book BPD in Adolescence? It is a very insightful and informative book by a leading expert in teen BPD, and even if your D15 is not diagnosed, much of what he describes is extremely helpful. (Especially the parts about the pros of diagnosing teens, what drives the manipulative behaviors, and validation, the key skills to master with an emotionally vulnerable child). There are also some youtube videos featuring Dr. Aguirre that might help you make sense of what's going on.
I just read an article that said BPD behaviors in adolescence seem to peak at 15, then tend to decline until 17 or so until plateauing between 17-19.
I'm glad you found the site

there are others going through the same thing (the holidays can be a bit quiet), so know that you are not alone, and that we are here to walk with you.
LnL