Hi bluemelon, and

Wow, that is quite a bit of drama your sister seems to be causing for herself and your family. It must be hard to watch a loved one find herself in such an awful relationship, yet on the other hand won't accept the help you and the rest of her loved ones have offered. And while she may or may not be suffering from BPD, her actions are obviously extreme and frightening, so I can understand the confusion you must currently be feeling.
It's curious how she would come to her own conclusion that she suffers from BPD, yet at the same time does not want to be 'labeled'. Sometimes an accurate diagnosis can be the key to healing, if one is truly committed. Is BPD something she has ever directly discussed with her counselors?
Bluemelon, please know that you have come to an excellent place for resources on dealing with loved ones suffering from BPD, as well as gaining insight from other members who have experienced similar situations in their own lives. Keep posting and telling us more of your story--we're glad that you've found us.