How well the gun fits you is important in felt recoil. Length of pull (the distance from butt to trigger) should be about the same as the distance from the tip of your index finger to the inside of your elbow. The rise of the comb should meet your cheek bone when your head is upright and your eye naturally sights along the barrel. Next is how you fit the gun. When your elbow is held out parallel with the ground your clavecal bone pulls back out of the way and your pectoral muscle rises up for padding and to create a pocket for the butt to rest firmly in. Body weight slightly forward to absorb recoil. Sitting at the pistol bench probably had you hunching forward which would rest the butt on the bone instead of the pocket, and I wouldn't doubt that for at least some of those shots that elbow was down resting on the bench instead of parallel to the ground. The whole point of a shotgun is versatility. You don't want to be restricted to just pooh butt loads. Try another shooting venue where you can use a proper stance.

Oh sorry, forgot to mention, for your wife, google Mirage 12 gauge shells. They have the lightest 12 Ga. target loads available I've found, and work great for the 16 yard line in trap. Shot several 25's with them. They'll be in clear shell casings, sorry I can't give you more specific info, I don't ever buy them anymore and it's been too long since I bought them last to remember the details.

Check a guns gun weight out....it is directly related to recoil. The heavier the gun, the less recoil. Only gas operated autos reduce recoil.
The lightest of loads are preferred for practice/trap. 1 Oz loads have demonstrated as good of performance as the heavier 1 1/8 oz. loads in 12 ga.
For hunting, the heavier hunting loads do not seem to be a problem for most shooters, as the excitement of the moment seems to dissipate the recoil effect.

The mule kick is why I went to an autoloader. Remingtons gas operated 1187 is a sweet gun to shoot. We shoot alot an my buddys all called me an old man and a sissy because I couldn`t take the kick anymore. That was 3 years ago and now three of the four have autoloaders. The big sissys.

Using all the other advice that guys have given you remember to bring the gun up to your face and not your face down to the gun.
To seat the butt into your shoulder if you are right handed raise your right elbow up until it is at least the same height as your eyes when you look right at it. This will automatically seat the butt into the pocket.

I shoot a 12 2 3/4 and it doesnt hurt I am 5'11 150 and 13 also I shoot a 12 same length slugs but have a good recoil pad on that but before that it still didnt hurt but a couple years ago when I first started 2 3/4 20 hurt with birdshot and slugs gave me bruises so you will get used to it

Get a slip on recoil pad and start with some light loads, I am sorry to admit that I have never shot a gun that had totally unbearable recoil so I'm afraid I really can't help much