Believe me when I say this, if she wanted to use/drink alcohol she would find a way to get the fix, bus, train, walk, hitch hike, skip or crawl. And, if she wants to find a way back home, she will.
People in jail, prison, rehab or detox all discuss the same things, that includes SLH, Salvation Army, how to get home, how to con others and so forth....they are master manipulators and your sister has been around the block more than one time. She has it all figured out, it's just a matter if the enablers will agree to her plan or not.
Go to meetings, read Codependent No More, both are a good starting point and read all the stickies at the top of this and the F & F of substance abusers, lots of good information at your fingertips.
We are here for you, keep posting.