Yes, it's a heartbreaking story, marxo. I can only imagine how helpless you must feel.
Beyond giving support, there is very little you can do for your sister. But you can get help for yourself during what sounds like a crisis for you. Individual counseling or therapy can help, and there is a drug users equivalent of Al Anon called Nar-Anon.
Someone will always be here and in the Friends & Family Forum as well. It's a good idea to get as much support as you can.
“The world we see that seems so insane is the result of a belief system that is not working. To perceive the world differently, we must be willing to change our belief system, let the past slip away, expand our sense of now, and dissolve the fear in our minds.” W. James