Recoil is not a problem for her. She shoots my 480 Ruger with 355gr bullets and loaded to near max. plus her favorite gun is a Colt Trooper MKIII in .357 magnum. She just wants something smaller for carry but she doesn't like 2" barrel guns. she just prefers a longer sight radius.
The .357 will recoil in the hand a lot harder than the .480 Ruger. Let's say you're shooting max 26.5 grain loads of Lil'Gun behind a 355 grain bullet. We'll used published 7.5" test-barrel data at 1531 fps, and a gun weight of 53 ounces typical of a Ruger. That gives:
Recoil Impulse 2.87 (lbs.sec)
Recoil Velocity 27.94 (fps)
Recoil Energy 40.03 (ft.lbf)
Now let's try a .357. Max load is 18 grains of Lil'Gun behind a 158 grain bullet for 1577 fps, but now our gun weighs 11 ounces, the lightest S&W .357 Magnum.
The Recoil Impulse is much lower indeed: 1.51 lbs.sec
but this isn't what you feel
You feel:
Recoil velocity: 70.48 fps -- the acceleration of the gun is MORE THAN TWICE the .480 Ruger
Recoil energy: 54.07 ft.lbf -- 35% more recoil energy than .480 Ruger
Practically speaking, the bullet velocities are going to be substantially different based on the actual barrel lengths. But just using the test data, you can see the .357 has the potential for a LOT MORE recoil than .480 Ruger when you get the "smallest and lightest" .357 Magnum.
Maximum 158 grain loads in my lightweight .357 Magnum with a 1.875" barrel did not chronograph at 1577 fps, but they went 1200 fps. How does the recoil compare at that velocity?
Impulse: 1.24
Velocity: 58.1
Energy: 36.06
As you can see, the recoil energy falls a little but short of .480 Ruger, but it's still extremely stout. More importantly, the recoil velocity is still MORE THAN TWICE .480 Ruger. In my experience, high recoil velocities are what make a gun the most difficult to deal with. They make for an extremely sharp jerk that is painful. Think about taking a fast jab from a lightweight boxer or getting hit with a fastball versus having a city bus slowly back into you. The bus has way more impulse and energy, but it's just going to push you back and won't hurt. That's why you want the revolver to weigh more like a city bus and less like a baseball.
With that said, I think the Ruger LCR is probably the lightest .357 with a 3" barrel. The S&W Model 60 might be next, followed by the Kimber K6S and then the Ruger SP101. My experience is with the S&W J frames. I have several in Scandium, Aluminum and steel. With reduced loads, they can all be shot well, but the steel guns are easier to do that with. By reduced loads I don't mean .38 Special +P, just less than maximum .357 Magnum. Shooting a 125 grain bullet at 1050 fps is more than any .38+P, but still only about 60% of a max .357 Magnum load.
K-frame S&W's are heavier than the J frames, but I think I prefer them for other reasons entirely. Because I can reduce or increase the load to whatever I like for a given weight, I don't dislike the J frames and similar size revolvers because of their lightweight. Instead, I dislike them because of their poor fit and the poor actions that are a result of compromise for size. The K frame action is better than all the mini revolvers, and the guns with longer barrels have a better sight radius, better sights usually, and a better balance.
The Performance Center Model 19 Carry Comp is a good example of what can be done to make a nice ~3" K frame carry gun. I think it is better than any of the mini revolvers. Personally, I would start with a Model 66 2.75" and do the modifications that I prefer, because if I bought the Carry Comp and still had to change the grips, the sights, and cut it for moon clips and didn't care about the compensator, then it's not a good value. But if it comes close to how you like it, then it's a good deal.