If she has really small hands then I would go with a Gen 4 in 9mm. In anything but the G26 the recoil from a 9mm is pretty mild. Also you can use G19 magazines in a G26, just add a Pro Mag grip spacer and you have a full grip on a G26 frame, the recoil is more noticeable than in a full sized gun but it's not that bad. That said, if your looking for a home defense gun, why not a shotgun? If your wife can't handle a 12 ga., a 20 ga. or a .410 will still fill the role better than any handgun.