Frequent Urination / Stinging at end of Urination

My mother, 74, fighting overian cancer - undergoing chemo treatments, tumor in pelvic area resting up against bladder causing her to feel like she constantly had to go to the bathroom.  Past three months dealing with frequent urination and burning while urinating.  Initially diagnosed with UTI and given Macrobid for a 2 1/2 month period. The stinging never went away.  Urinary Stint placed in two weeks ago.  Urinating more frequently (every 1/2 hour to 1 hour).  Still burning at end of urination. Now told that it isn't a UTI but it is the stint that is causing the discomfort and that she needed to give her body two weeks to adjust to the stint.  Two weeks have passed and the frequency and buring is as bad as ever.  Does anyone have a differing view on what might be causing the problem?  My mother is suffering greatly because the frequency of urination is keeping her from being able to sleep.  Could the situation be misdiagnosed?  Please Help!