It doesn't get much simpler that the Stoeger coach gun: http://www.stoegerindustries.com/coach-gun-supreme-shotgun If your wife is going to shoot it they make one in 20 gauge.
Other than that the Rem 870 or Mossberg 500. Both good just different. I used a Mossberg in the military and I prefer the location of the safety over the 870, but would upgrade it with an aftermarket aluminum safety if I went that direction. My go to home defense shotgun is a Police model 870 that I sent in for the Vang Comp treatment. Used 870's can be found on the cheap and upgraded over time. But the Stoeger is super simple to operate. http://www.tactical-life.com/firear...gnum/#tw-dc-remington-870-police-magnum-bahde
Other than that the Rem 870 or Mossberg 500. Both good just different. I used a Mossberg in the military and I prefer the location of the safety over the 870, but would upgrade it with an aftermarket aluminum safety if I went that direction. My go to home defense shotgun is a Police model 870 that I sent in for the Vang Comp treatment. Used 870's can be found on the cheap and upgraded over time. But the Stoeger is super simple to operate. http://www.tactical-life.com/firear...gnum/#tw-dc-remington-870-police-magnum-bahde