Get her urine culture test done. A long standing non treated UTI can cause this. Also, consult a gynec with the culture report. Dr Sachin Dalal

Maybe due to urinary tract infection as you are saying sugar levels are under control....Urinary tract infections can be painful, but you can take steps to ease your discomfort until antibiotics treat the infection.....Drink plenty of water. Water helps to dilute your urine and flush out bacteria....Avoid drinks that may irritate your bladder.... Avoid coffee, alcohol, and soft drinks containing citrus juices or caffeine until your infection has cleared. They can irritate your bladder and tend to aggravate your frequent or urgent need to urinate....if no improvements Consult nearest physician they will help you further..