Bathroom

I have the same condition.

I found using a cane very helpful to overcome the transitory balance issues.

A shower stool also helps to sit when taking a shower..

When our then paraplegic teenaged granddaughter traveled with us in our Coachmen Cass A, we used a modified shower bench and walker for her showers. I've also seen walkers with a built in flip down seat that might also work.

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.

As long as you can tie into the structural studs or put some blocking in a wall to attach a rail. Have you considered a shower stool? Can be found at any medical supply place for your exact purpose and most fold up for easy storage.

A floor plan would help. Grab bars can be secured to the shower wall but if you have access to the other side of an abutting interior wall, you can beef up the location by removing some interior wall panels and installing some extra wood on the backside of the shower wall.
If you have room, how about a shower bench also?