Hi Sadmummy, adding my voice to the

Teen years are hard enough already without the addition of BPD to the mix. You do sound like you're at the end of your rope -- glad you found us.
Like CC43 mentioned, DBT can be helpful for pwBPD who choose to participate and engage. It's one of a few evidence-based therapies for BPD, so if your D17 is currently compliant (more or less) with appointments, then I would hope that bodes well for her participation in DBT -- though time will tell.
Are you currently in a relationship? If so, how is your spouse/partner doing with things? And do you have other children at home?
I hope that in all this focus on your D17 and her needs, you are also able to take some time to care for yourself. We can't help others when we have nothing left in the tank.
While my H and his kids don't have BPD, his kids' mom has many traits, and that makes family life challenging. I'm currently on the waitlist for the
NEABPD Family Connections program, which is a free online program for family members of those with BPD. It focuses on skillbuilding for more effective relationships, so do take a look at that and see if it sounds like a good support for you.
Keep us posted;
kells76