Hello Tnb. Glad you found us... .sorry you had to. : ((
First of all, if you have spent any time reading posts on this website, you will realize you are not alone. All of us have been the best parents we knew how to be... .never thinking "this" would happen to us. After about 40 years of dealing with our ubp daughter, I still shake my head.
Certainly your situation cannot go on the way it is but it is you who will have to make the changes. See Lesson 2

"If your current approach is not working - change it."... .for starters.
I would strongly recommend that you and your husband track down a good counsellor... .for yourselves. That would be someone who is familiar with BPD. You need a professional sounding-board to help you along the way. It is not "power" that you are needing... .instead it is the need to be "empowered."
Our daughter has played havoc in this family... .used us... .verbally abused to the point where we are now n/c with her... .our choice this time. It would have been good years ago if we had found the tools/information that is available now.
No one here is going to tell you that life is going to be easy with this adult child of yours but gains can be achieved... .especially for you and the rest of the family. Your worlds should not pivot on her moods. She has to take responsibility for her actions and any consequences that follow.
Hope to hear more from you TNB. While people here will help by giving support... .sometimes suggestions... .your posts are important to others who are needing the same kind of support.
Huat