Be sure that the shotgun is cut down to fit your wife! A too-long length-of-pull, even with light loads, will absolutely beat her to death. We've had ladies who were going to give up shooting while sharing their husband's shotgun. Then they used my wife's gun and loved it. Make sure she leans into it so her body absorbs the recoil, and holds the gun
tightly against her shoulder.
Even though you didn't mention it, don't get her a 20 gauge unless you load your own shotshells. Until Winchester actually starts producing their 20 gauge Winlites, the combination of a relatively light 20 gauge shotgun and relatively heavy available commercial loads results in MORE felt recoil than a 12 gauge with Featherlites.
Placitas Slim is right about the Featherlites. That's what we shoot also. The "Featherlite" monicker is what most shooters call the load, because there's a feather on the box and on the shell. They are marked "Low Noise, Low Recoil," and the Winchester number is AA12FL8.
My wife shoots a Coyote Cap/IAC '97 and a Stoeger SxS, both cut down to 12 1/2" LOP. I can shoot 'em, but I have to have my thumb surgically removed from my mouth afterwards....