Hi MiaP,
You sound like a great mom, wanting to do what's best for her

It's too bad that she isn't receptive to counseling (I had similar feelings at that age). You can, however, continue to offer her support. This book can be of help to you:
The Power of Validation (for parents) - Karyn D. Hall, PhDMany of us here have found it immensely helpful talking to our kids.
I think of myself as a good validator, and I've always been good with kids (I was an at-risk teen youth mentor before I met my ex), but I picked up a lot from this book.
The communication tools in Lesson 3 on the Improving Board are meant for pwBPD, but they work on anybody. I'd suggest looking there as well (SET, validation).
It sounds like you're already a safe and trusted adult to her, and being heard is one of the number one things that teens need... .which they take as being both valued and loved.