LPguy:
.357 Magnum was invented by I believe it was Doug Wesson in about 1935. The name of the cartridge comes from the fact that Wesson was also a wine coinnessuer. A Magnum bottle is a bottle which is slightly extended.
The catridge was an effort to improve on the .38 Special. At first they simply made a heavier revolver and loaded the .38 Special a lot hotter. The problem was though, predictably, a bunch of goofballs wanted to use the new hot ammunition and loaded these super hot new catridges into their old guns and got a nice kaboom.
It was decided that the cartridge had to be elongated to visually and physically distinguish it from .38 Special. Notice if you put a .357 Magnum catridge in the cylinder of a .38 Special revolver, you can't close the cylinder. The name comes from the fact that the actual caliber of the bullet is .357 of an inch. ".38" is just a naming convention the origin of which I do not know.
Thus a .357 Magnum is just a lengthened .38 Special that's been loaded hotter. So yes, you can fire .38 Special in a .357 Magnum chambered revolver just not the other way around.
Now we're getting into why I love revolvers so much. A quality .357 Magnum revolver gives its user many options in ammunition. If this is a heavy steel gun, just about any .38 Special should have very mild recoil.
What helps tremendously are the right grips. Wood grips are lovely and all, but soft tacky rubber Hogue grips are what a "combat" revolver really needs in my experience. That's what works for me though. People who are uncomfortable shooting revolvers are most often the same people using wooden grips. I personally find wheelguns offer their owners a lot more options when it comes to grips personally. Wood grips do look nice and may feel real good to hold, but my personal experience is that they slip. Rubber also "gives" a little bit and won't fatigue your hand.
I do know pretty much any .38 Special load fired out of my 686 is very soft on recoil and I can't imagine anyone would not be able to handle it. The only thing that makes this revolver intimidating to some people is that it's a pretty big and heavy gun if you have small wrists and small hands. That's why many shooters prefer the K frame models.
Most cheap 110 grain .38 Special cartridges like those from Winchester's White Box offerings should be pretty mild. The "idea" practice round for me is a 158 grain load. I personally can't feel a difference.
Edit: Also, if she's flinchy, avoid the Magnums like the plague. There's not a lot of .357 cartridges that don't spit fire. It also helps to have them shoot in broad daylight. Have her shoot at dusk where she can see the light show and I promise you she'll drop the gun.
.38 Special out of a 4" or longer barrel is not to be discounted. My mother's designated gun is actually a .357 Magnum revolver loaded with some 158 grain semiwadcutters. She has pretty bad athritis of the fingers and is thus genuinely recoil sensitive and not just flinchy. She can fire the entire cylinder if she has to, but extended shooting would be too painful. But I figure if she can handle it, just about anyone should be okay.
