All kids must nap here until age 3. My daughter quit napping at 3 but all other kids kept napping until aged 4. I even quit napping a 5 year old this summer so that she could be ready for kindergarten (and she never slept anyways) and her mom didn't want me to! LOL
I would tell the parents that she must lay down for one hour. If she falls asleep then you will not be waking her up. If she is awake then you will get her up and she can watch tv/look at books/do puzzles for the second hour but must be quiet.
This is your home and your rules. There is nothing wrong with a child going to bed at 8pm. My daughter has always been in bed at 8. I never understood how anyone could put their child to bed at 6 or 7.