Hi sacparent
I am sorry you have been struggling for so long.
It is difficult to pinpoint certain behavioural patterns particularly when your child is a teenager -most people don't have an understanding that some things teens do are not normal teen behaviour!
As a parent though, you know when something is not quite right.
i am glad you are trying to get to the bottom of what is really happening with your daughter.
It's also understandable that you are sad that it is at times easier to be without her than with her - pwBPD can really push our buttons.
If she does indeed have BPD then you may need to find very different methods of relating to her than you have previously used.
As far as bringing up your suspicions to her, I would strongly advise not to do that as yet.
Firstly you want to educate yourself as much as you can on the disorder to be really sure that this is what you are dealing with.
Another important thing is that pwBPD do not always accept that that is what is really going on and it can drive them further away.
I would advise you to look closely at the things you can do to manage your own responses to her and learn some communication tools
first.
If you have not already read them yet you might find it useful to examine ways to improve communication an reduce conflict.
here are some links:
Tools to Reduce Conflict with a person suffering from BPD (3 minute instructional video)https://bpdfamily.com/portfolio-childI hope you will find them useul
Ziggiddy