she has told me to get the heck out of her business
A dear friend of mine has a daughter about your daughter's age who's an addict. I don't have any first-hand experience of an addicted child, but seeing my friend struggle with similar questions, I've drawn the conclusion that it's more difficult to detach from the recovery of your child than that of your spouse. To me, from the outside, it has seemed like the entire detachment idea goes so contrary to everything your instincts say as a parent that there's one more giant hurdle you have to get over.
My friend made the decision to pay for treatment and stay out of
how her daughter did treatment & recovery. She did tell her when she went into rehab that this was the last time she would pay for rehab; that she would stay the course until she "graduated" from a sober house and found independent living, but if she chose to relapse, she would be on her own.
I have no advice to give you -- on the one hand, I can see how you feel that if you are footing the bill, you have a right to know that she's utilizing the full spectrum of services you are paying for. On the other hand, there's the truth that you're already aware of that you can't do her recovery work
for her.