What is a grandmother to do?

My daughter has a 3 year old that is overweight and is very destructive. When she comes over we don't let her just do anything she wants like she can at home. When my daughter came to pick her up, my granddaughter was doing something destructive that she knew she wasn't suppose to hoping she could get away with it when her parents were here. My daughter got mad at me when I told my granddaughter that she was not allowed to do it. What is a grandmother to do?