Dear Karolina,
That sounds very worrying. I think (and this is just my personal opinion) that you are right to think that subtsance abuse can be the sign of underlying problems. These sorts of problems can be difficult to admit to ones self, let alone a doctor or family member. Once these problems lead to drug abuse, then of course that opens a new set of very complex problems in their own right, very serious ones potentially, and this can be the cause of many others. So its easy to see perhaps why your sister blames drug abuse for her troubles.
It must be very frustrating and worrying for you to be physically removed from the situation. From what you say I think you are definitely right to be concerned and to beleive that your sister needs professional help.
Like I say, BPD is a very serious diagnosis and can only be made by an expert psychiatrist, and really only by one with specialist knowledge of that specific disorder. A specialist specialist if you like. It is unfortunately that your sister refuses treatment. Does she give any reasons why she refuses treatment? Its a very common problem, especially with substance abuse. Help can seem just too difficult to accept sometimes.
I'm glad you have found help on this forum. I am not a psychiatrist, or a medical doctor (I am a neuropharmacologist, a specialist in brain chemistry- so far removed from patient care), so I am not qualified to advise you on this problem. All I would say is that alternative therapists aren't either, and really should admit that, or risk doing more harm than good. They are definitely not qualified to diagnose or treat such conditions (and, as I say, must admit that).
It really sounds like your sister needs professional help. But of course there is only so much you can do. She has to decide to help herself at some point, and that begins with accepting the help that is offered.
All is not lost, people can turn their lives around from almost any situation. She is lucky to have people who care. I think that is more important than anything else.
I wish you all the very best.
H