Suggest Remedy For Urinary Problem

My step-daughter constantly has to go to the bathroom, she can barely hold it for 45 minutes. Sometimes not even that. She has had accidents. She gets up 2-3 times a night to go. Recently, i heard her going and it's like a splash of urine and that's it. Even if she hardly has to go, she barely makes it to the bathroom. she never wets her bed, but she has had accidents during the day when she has tried to hold it. She is 9 about 90 lbs and has been tested multiple times for bladder infections and such, always negative.