Hi bella and welcome.
I am really sorry to hear of your daughter's issues, and the confusion and frustration that this is certainly causing you both.
There are certainly possibilities as to a dx or BPD or other mental health issues. My oldest daughter has been dignosed as Bipolar 2, and there are similarities that pop up in reading your account of your daughter's behavior. (attention seeking, becoming angry when other's don't react according to her expectation/will.)
However, only a professional who has worked with her for some time can fully assess the situation and properly diagnose the issue.
I believe that the best move that you can make at this point is to continue to encourage her to go to the therapist. Try not to make any personal judgements or hold opinions as to what is going on...simply support the effort to get help, remaining neutral as possible.
I have to be very careful in how I talk to my own daughter about
her issues. Since she was also diagnosed as an adult...it is up to her to own her treatment. I am simply there to be a support system.
That is not to say that I put up any innapropriate behavior on her part towards our family. She knows that there a boundaries and limits as to what we can and do tolerate! However, we are there to help her navigate through the things in life that she finds difficult as a young adult with her issues.
I would encourage you to look into getting educated on the things that her therapist suggests. He/she may not be able to divulge details of what goes on in the session...but if you ask, I am sure that he/she could point you in the right direction as far as what to reasearch.
NAMI would be a good place to start. http://www.nami.org/
I wish you the best. I will keep your family in my thoughts and prayers. Post with us anytime.