Bladder Training for Elderly

My 93 year old grandmother has a fixation with needing to use the bathroom.  She is living with family members and insists on someone helping her with frequent bathroom trips.  She ambulates to and from with her walker independently but needs assistance moving from sitting to standing positions.  Frequently her trips to the bathroom are only minutes apart, and most often not productive no matter how long she stays on the commode (sometimes 45 mins to 1 hr).  She has had a recent urology work-up and there is no physiological reason for her frequency.  The family believes she is using these trips to maintain her control in the household.  Trips to the bathroom occasionally spiral into a battle of wills.  I suggested setting limits buy setting a timer for every two hours, after first explaining to her that she will be given assistance only every two hours.  Her expectation for assistance goes on around the clock, night and day.  She does not seem to be driven by a fear of being incontinent, since having a wet bed in the morning does not seem to upset her.  Her obsession with the bathroom is exhausting the caregivers.  Any advice for getting out of the bathroom with Grandma?