Welcome Gema: I'm sorry about the problems with your daughter and your family situation. Could your reference to "hits" mean that your daughter is
SPLITTING (Painting someone black)?
I have set up a time and date to try and talk to my daughter again because my granddaughter is angry I have cut off her mother and is accusing us of ruining her wedding that is this summer.
In what way would you be ruining your granddaughter's wedding?
Is it possible for you and your daughter to have a joint therapy session with a neutral therapist? It seems to be common that people with BPD traits think that the problem is always with the other person. It isn't necessary to have a diagnosis to try and make things better.
Unless your daughter wants to change, she won't. The only thing you can do is manage the way you communicate with her and how you react.
You might find this information helpful: FAMILIAR FIGHTS: - Projection, Splitting, Emotional Reasoning and Blame There are some helpful links in the margin to the right of this post. If you look at the "Tools" section, you will find information on some helpful skills to use with your daughter. Check them out and let us know what you think. It can be helpful to practice some dialog in a therapy session. It can be a good combination to use your therapy sessions and interaction her to help you get confident in some of the communication skills. Validation (or don't invalidate) and SET can be two skills to start with.