You're being such a good sister, very supportive. At times like this, it's easy to forget that we aren't responsible for their recovery or their program any more than we are responsible for their "slips" or their addictions. She'll remain sober if it's her time and she's ready to really work for it. She'll go back out if she's not done yet. And all you can do is love her through it.
One day at a time - for BOTH of you!
Hugs
Cats