I think my daughter may be younger than yours (mine is 17) and I can relate with so much of what you've said.
She was kind of diagnosed at 14, her first hospital stay. I say kind of, because as you're probably aware, doctors are reluctant to diagnose. We had a wonderful psychiatrist who asked me to do some research on my own about BPD, and to let her know if anything resonated. I really appreciated that suggestion...so she wouldn't "get in trouble" with her colleagues for diagnosing, yet she was validating the behavior, symptoms.
Anyway, you've described very well, what it's like with my daughter. Silent treatment for weeks. A vacation (rented a home to be Covid-safe, etc.) was virtually ruined, because she decided that something I said warranted the silent treatment. She also stayed up all night a few nights (good about taking day time medication but has bouts of not taking her night medication and therefore would not sleep), and was falling asleep during tours, etc. When she later told me the "infraction" I'd done to warrant the silent treatment, I was floored. This is when I began to see that the lens that she sees relationships/the world through, is so very altered. I don't understand why/how she can joke with friends ...and her friends can make an innocent comment here or there and she's fine with it, but if I say the same thing, I'm horrible, insensitive, traumatized her, caused her illness...you get it.
The first time she verbally attacked me she had me in tears. It was so confusing, and twisted and confounding. She was relentless. No empathy at all. The way she (and it sounds like your daughter) rewrite the past to make it as though we were neglectful, hurtful mothers. You (like I) know of all the supportive and good things we've done, and to have our daughters malign and blame us, and to have reason to believe that they're slandering us to others is heart-breaking.
I felt good when I heard that a friend of hers took up for me and said, "your mother isn't like that." It meant so much. It's hard knowing that new friends that she'll make, won't have a frame of reference, and will likely believe that I was some sort of horrid mother that caused her mental illness. That really bothers me. I'm far from perfect, but to have folks think the worst of me... Yes, I know the truth, but I'm not sure how to not be bothered by negative things put out there in the world, about me.
I finally decided to reach out to a therapist, for me. We had an initial consultation and agreed that I could make appointments as needed...kind of like crisis management. I feel isolated sometimes because how in the world do you explain this to friends? It takes as much energy to explain and defend my daughter (since she DOES have a mental illness) as it does to shore myself up to deal with her.
One thing I'm struggling with is the future. It's hard to try to not live - like the other shoe is going to drop. Just waiting for something bad after something bad. Even when things are good it's like you can't just collapse yourself into the good. I have a strong sense of humor and appreciate good times just like the next person...it's just that well, for example, longevity runs in my family. My mother is 98. Sometimes when I think of living a long life...THAT can make me sad. I don't want to live life on these terms. I'm not saying I"m suicidal...I'm saying that it's daunting, to think that life is going to be this way. So that's why I decided to seek a therapist...to try and find a way to live my best life, even with periods of well,
PLEASE READtiness.
I say all this to say, that I can relate to you...and appreciate this message board, very much.