Member of an unknown family sharing plan

I want to add my daughter into a family sharing plan. I have sent her an invitation but after she tries to accept it a message showing she's already part of another family sharing pops up. I go to her AppleID setting and click the family sharing, then a message telling me an adult is needed to enter that setting shows up. She doesnt what family sharing she's part of and there's no way of finding out or leaving that plan, at least not through her AppleID. Any ideas?