That is very good advice from Tryingtobeme, support is key. Since you have no official diagnosis it is vital to get one so that the right treatment can be offered. But you are doing a very good thing and she is lucky to have you. If she does have BPD as I have it is quite likely that her relationships with people will be quite strained and it is not necessarily her fault she just learnt how to communicate and share the wrong way. But if you can get her to see a therapist and she is diagnosed with BPD I would then look into DBT therapy and read up on the work of Dr Marsha Linehan she is one of the foremost experts on BPD. DBT is Dialectical Behavioural Therapy and is very supportive and basically helps a person to become less extreme and manage their emotions more effectively because in short it is our regulation of our emotions that is the most common problem. I wish you luck and all the best for a good outcome

Paddy