As women age, the bladder and perineal area go through changes, making UTI's more likely. There are many reasons for this, which include loss of estrogen and changes in the
bacteria that live on the skin. I am glad that she is drinking well,. Frequent toileting, which you sound like your doing, can be helpful. Since she is still incontinent, make sure that she is properly cleaned after each incontinence episode. This is especially important if she is incontinent of stool.
You mention that she is on Detrol, which is supposed to reduce her incontinence. Sometimes this medication can cause the bladder to not empty all the way, so I would ask her medical provider to check that out. This can be a common side effect of this medication, especially in people who have bladder problems related to strokes. If her bladder doesn't empty well, then that stagnant urine can cause a UTI.
Some people swear that cranberry juice or Vitamin C help by making the urine more acidic, which can help reduce UTI's. Medical research has not really proven these claims, but you could try it and see if it works for your mother.
If the infections continue, then you can talk to her doctor about suppressive therapy for the UTI's. This consists of a daily dose of antibiotic that sometimes helps reduce UTI's.
Hope this helps. Good luck!