I hate it when things don't go the way you would want them to.
The good news is that, hopefully with the help and support of her counselors/ social workers, she can be talked into not only finishing her work at the rehab, but going to a halfway house from there, if she can find a good one. Then you can have that much more time with her daughter, and it just may be what her daughter needs to stay strong. If she can stay sober long enough to see how much this is hurting the girl, maybe she'll be more motivated to do what she needs to do.