Hello wandell, welcome
Glad that you are here looking for ways to help support your uBPDD (undiagnosed BPD daughter).
You say that she is very sensitive, has struggled with relationships and has strong black/white thinking, there are tools to the right

that could help. Maybe you could look at Validate the Valid, to help with her sensitive feelings. It is her feelings that need to be validated not her thoughts or actions, so could be a good starting point for you x