What Causes Urinary Incontinence In A Child?

I have a 5 year old niece who's been urinating on herself for the past 4 months got ultrasound and x-Ray done to check her kidneys and results came out ok but she complaints whenever she pee when she takes medicine for the infection it goes away but after a couple of days she stops taking it it comes back it also smells fishy what can we do fa mil y concerned please help.....thanks.