Welcome, and yes, many things our loved ones say or do make no sense at all. My adult daughter has pretty much alienated all of her siblings and no longer has her close friends that she had through out her high school and college years.
What I have found that has been very helpful is reading and re-reading as much as I could on validating her, and what to say when she is very dysregulated. I went as far as copying and pasting some of the key phrases so that when she called, I was ready. I also learned to say " I can hear that you are very upset, and I want to know more, however, I need you to stop yelling, or we will have to continue this conversation later." I only repeat that once, and then if she continues to escalate, I usually say something along the lines of " I can hear that you are very upset, however, you are still yelling, so I will talk to you later when "things" settle down." This has worked very well for me, even so much as the last two times she has gotten escalated, she has called back hours later to apologize. That was something that never happened before.
I also have found that because I am her one constant person in her life, that I make a point of checking in every day, just to say hello. This has also been helpful because I find that things don't escalate and brew for as long. I honestly used to dread talking to her, but that is not the case anymore.
My daughter refuses any counseling at this point, which I can understand b/c she has never had the right kind (DBT), so I am now working on reading the DBT workbook in hopes that I can help her with some change strategies. I don't know if that's even possible, but I am going to give it a try.
I have also found these recordings very helpful ( I even copied and pasted some of her responses). Hope some of this helps- keep us posted.
Family Connections: Must-Have Skills (October 16, 2011)
by Marie-Paule deValdivia
https://www.borderlinepersonalitydisorder.org/recordings-for-families/