Sorry for the delaying in answering as I have to go off line.
Thank you for the information.
Infection is the most common cause of frequent urination.
Though she has been tested for it , still repeat tests for routine and culture often necessary to confirm it.
Vulvovaginitis which often is the possible cause of frequent urination in female child.Allergy
to soap, pinworm, back to front wiping etc. can cause vulvovaginitis.
Other cause can be pollakiuria where mostly children of her age usually affected. In that case of no sign of infection is detected. The child can go to toilet 20-30 times a day. Usually no cause is found. Stress can be the factor of it. Over times it goes away.
Voiding dysfunction can occur too in this age group. The child can not complete pass urine when she / he goes to toilet. You can check it whether she is having the condition. In that case proper toilet training
will be required.
Consultation and regular follow up with pediatric nephrologist is necessary to find out the exact diagnosis.
I hope this information will be helpful.
Please ask if you need any clarification.