I avoid giving advice, and normally phrase everythign as a story, suggestion, or question. In this case, unless a lawyer tells you otherwise, please assume you are on the hook for this debt and give the check to the treatemnt center.
The consequences of not doing this could be considerable, and I don't count it as controlling her-- I count it as controlling yourself and that's allowed.
Take what you want and leave the rest.
Cyranoak