Hi Gerri
That sounds heartbreaking, after making progress to have yet another setback. Its really good she trusted enough to come home before doing something more dangerous/damaging. I'm not sure how addictive Valium is but hopefully she can face that possibility with therapy and get off of all dependency.
I think, that if she is home, physically ok, mentally there and going to therapy, there is hope that she can learn from this and face it and move on. If she has accepted that she is recovering from BPD that is really huge, and is a responsible step to take. Sounds like you and she both need support right now - are there family and friends you can turn to just to vent and feel support?
If you've supported her through the journey to stop drinking and get her degree, then you're doing something right. And if she did those things, then overall she is too. Hoping for the best now,

just keep plugging and doing the best you can, it means a lot I think.