With ladies, one thing to be aware of is the stock's length of pull. If your wife is short (like mine at 5'3"); a Youth Model shotgun maybe a good fit. Otherwise, the normal stock sizes will be awkward and cause an unpleasant recoil experience. My wife shoots a Beretta 20 Ga. Youth Model semi-auto, but many other choices are available in semi-auto, pump and even, I believe a few O/U's.
You could also buy a O/U with say 26" barrels and have the stock shortened and fitted to your wife by a gunsmith.