I agree: a pistola...but a laser sight is essential.
IMHO a reliable semi-auto chambered in 9mm that you and your spouse are trained to use is the best first line of defense. A handgun can be kept more discretely in the master bedroom and is therefore more readily available on short notice, such as when an uninvited guest is breaking into your home. A laser sight takes the guesswork out of where your shot is going to go, and is probably more intimidating on the bad guys chest than the sound of racking a shotgun, which only gives away that you don't have a shell in the receiver. A handgun is much easier to maneuver inside the confines of a home, is easier for a woman to handle and has much less recoil. This debate of shotgun versus handgun will go on forever, but with customized laser grips and sights becoming available for many popular semi-auto pistols, I think these are winning out. You still have to aim the shotgun since at short distances, the shot will not spread very much. And, at short distances, you will be more accurate with the handgun-laser combo that you don't have to aim. Two quick rounds to the chest should give most bad guys pause, with the possible exception of a crazed 300 pounder who will need more discouraging. That being said, I have both, but I know I can get to the pistol much faster and be ready for action before I could even begin to think about racking the shotgun.