cglass, I really understand your pain and what you may be going through. All you can do is keep doing what you are doing. I know how much it hurts with our children and addiction. I found out the hard way.
At the end of the day, you have done all you know how to do and it is now up to her totally. If she really wants the kids back and she really wants a good life she has to make that final decision. As hard as that may be for her, you have to take a step back, a step forward and another step back. Let her know you love her and give her a hug when you see her but do not enable this habit of hers. Sounds like she has plenty of others to do that for her. You are her mum, so set the boundaries and she will know she can always come back to you only for positives.
My son and I have a silent understanding now. Its like we both know what the other thinks or knows and it has balanced somehow.