Any words of encouragement out there?
Focus only on what you can control. Your BPD kid is far beyond your control; she has to live her own life and you shouldn't stake your happiness on her instability.
You said that she "tries to get help" and "nothing seems to be working." Think about that. It's like me having a toothache and saying, "I don't know what else to do. I walked to my mailbox, took a multivitamin, and did some pushups. Yet my tooth still hurts and I'm so miserable!"
The way for your daughter to move past this isn't "trying a few things" that feel comfortable to her. It requires a committment to therapy, medication, and self-reflection. Until she is ready to go all-in, things will continue to be troubling.
And that brings us back to my first point- focus on what YOU can control. Your happiness can't be tied to anyone else; it has to come from within. Right now, you are okay...but you're letting your daughter influence far too much of your life. That's the real problem here and it's a "you probem." You have to let that illusion of control go because you're not in control of anything with your kid.
I hope that helps.