could my 7yr old daughter wet the bed because of how hard she sleep?

Yes, being a heavy sleeper may be a contributing factor in bedwetting. Limiting fluid intake and waking your child to go to the bathroom can be used with some success. The good news is that in most cases children grow out of bedwetting as their bodies mature and develop. If your child has seen a doctor or pediatrician, and no specific cause has been found, than the issue should resolve itself in time.