Hi Bananatree,
Welcome to the group

Though none of us can diagnose BPD, I like you am here because in my totally unprofessional opinion my partners ex-wife exhibits BPD traits.
It sounds like you care about your friend but are finding yourself getting burntout in terms of her issues. Self-care is really important when you have someone with BPD or BPD traits in your life. It's like when you're on an airplane and the flight attendant does the oxygen mask demonstration. They tell you to put your mask on first and then assist others. Why? because you are no help to anyone else if you are unconscious. It's the same when dealing with someone with BPD if you are emotionally exhausted you can't help your friend. It is important that you take breaks and take care of you.
I've pulled a link that relates to your post that you might want to check out... "Why are therapists hesitant to give a BPD Diagnosis"
https://bpdfamily.com/message_board/index.php?topic=68149.0I also pulled another link about the "Does and Dont's in a BPD Relationship" I know you aren't in a romantic relationship but much of the information still applies...
https://bpdfamily.com/message_board/index.php?topic=62266.0I'm so glad you decided to jump in and post. I have found this site and it's members very helpful when dealing with my Partners undiagnosed BPD ex-wife (uBPDxw) and know this group can be of help to you too. Please take a look around, if you are like me you will be amazed at how similar our stories can be.
Take Care,
Panda39