T.M.
My guess would be that she isn't having accidents at school because of the structure. They don't usually ask if you have to go to the bathroom. They go as a class at regualar intervals. Perhaps putting her on a schedule at home for a while will help. Like every half hour or every hour she needs to go in and try to potty whether she wants to or not. Just a suggestion. Not sure if it would work or not but it makes sense to me. Good luck, Shannon
PS. Make sure that she isn't being bullied at school or on the school bus. This can cause problems at home as well.