Marle,
Generally speaking, rehabs verify benefits before accepting a patient.
Most insurance policies require an adult child to be a full time student to be eligible for coverage on their parent's policy. Because of fraud, insurance carriers now almost always require proof that the insured student is indeed a full time student, in good standing. This does not happen until well after the fact.
I am wondering if this might be a part of the problem.
( This bit us big time when we learned that AD never bothered to attend a class and in effect was deemed uninsured. )