I would strongly recommend the North Rim. It will be cooler, less crowded, and quieter there. The campground inside the park is no hookups, so keep that in mind, depending on your needs. There's a couple of FHU campgrounds at Jacob Lake, which is about 45 miles north of the North Rim Visitors Center. Since your wife has limitations there are still points of interest to see, that would not overly tax her health, and to which you can drive for photo ops.
From Kanab I'd highly suggest you go to the North Rim of the Grand Canyon for a day trip. Have lunch at the Lodge overlooking the canyon and just outside the Lodge starts an easy trail out to a point overlooking the canyon.
These are great suggestions considering where you will be coming from, and especially is your earlier visit to the Grand Canyon was at the South Rim. We stayed out at Jacobs Lake and made the drive into the North Rim. Got beautiful sunset photos from the lodge, and then had a very nice supper there before returning to our trailer. You can drive along the rim and find many places to just get out, enjoy the view and take photos. This might be very good for your wife. After all these years, we still find our memories of the North Rim a highlight of our twenty years of RV traveling.