After about 5 shots with the Mossberg 500 w/ pistol grip, you will not want to shoot stockless anymore. Shoulder-less recoil is pretty nasty.
I would highly recommend that you consider purchasing a Knox recoil reducing Special Ops stock for about $100. It will make your Mossberg 500 a lot more practical for home defense and game shooting (and a lot more fun for your wife to shoot!). Only one allen screw to swap out.
You can also look for tactical loads, which have the same number of pellets but less powder. They have less kick and less penetration then normal 4 buck or 00.
A good recommendation on the Spec-ops, get the comb as well. The breachers grip replaces the pistol grip that came with it. One-handed slug shooting, made simple and painless.