6 year old wetting herself

[nis123]

My daughter will be 6 years old in June and starting school in August. She has been out of diapers since 2 1/2. She started kindergarten at almost 4. Before this she never wet herself. She had the occasional night wetting. She knows how to use the bathroom. We took her to the dr who then put her on " minirin" for 3 months to help at night, and now she is back on it for another 3 months. She was sent to do an ultrasound to see if it was anything medical, that was ruled out. She still is wetting herself at night. She wets herself at home and at the kindergarten. She has 2 younger sisters. One is 3 and the other 1 1/2. She fights a lot with her 3 year old sister, but not the 1 1/2 year old. They all play well but fight just as much. We have tried everything we can possibly think of. When watching telelvison she would wet herself rather than just take 2 min and go to the bathroom. Same thing when playing. her 3 year old sister is now out of diapers one week now and we hope this may help the situation. Please help with some suggestions...i need this to end before she starts school if possible. When asked if she knows why she wets herself she jsut says.."i don't know"