Over the years, we have been up/down Shafer Trail over 20 times in a variety of different vehicles in both summer and winter. Based on watching YouTube videos, I can understand your wife's concern. The scenery is spectacular and there is quite a change in elevation but I would assure her that it is a safe and relatively easy trip. They keep the trail nicely graded and it is fairly wide in most areas. There are a few tight turns that will require a back-and-fill maneuver, but nothing dangerous. A short distance from the bottom of the Shafer Trail you will find Musselman Arch. If you are exploring the Island in the Sky District, a trip down Shafer as far as Musselman and back up makes a great side trip with many photo ops. BTW, you can do some dispersed camping in the BLM Lone Mesa area on your way into the Island in the Sky. PM me if you would like your wife to talk with my wife about the Shafer Trail.