The positives of having involved grandparents outweigh almost any problem. I’m convinced that children know that “grandparent rules” differ from “parent rules.” If something is entirely unacceptable to you, make it clear (for example, 10 p.m. is the absolute latest she can stay up), then plan to resume your routines once she returns home.
The medication issue, however, warrants serious discussion. Offer the grandparents books about ADHD or set up a talk with your doctor. If the grandparents still refuse to give the medication, invite them to your home, but tell them that your daughter can’t stay with them.