Sorry to hear of your wifes condition. I recently looked at my shower and it appears to have some caps over the fasteners. As the others have said, you need to find the studs. If you get it opened up you may also be able to add horizontal blocking to give more variety of handle locations. When my father was ill I installed some in their shower per the recommendation of a nurse and the bars were at angles, not necessarily vertical or horizontal. You can find info on line. Pay attention to her grip size as far as diameters also. I hope the best for her.