`Well you really need to get her involved. What we think really doesn't matter half as much as what she thinks.
A few questions that she needs to consider though are:
Does she really want 357Mag? Having a bunch of power is nice, if she finds that she can control it adequately. I know that my mom was far more comfortable shooting 38Special or 45acp than 357 Mag.
Which grip fits her best and gives her the best control. Again, control is more important than almost all the other considerations. Let her hold and shoot as many different grip sizes as possible and pick the frame SHE shoots best.
Let her play with opening the cylinder and reloading. For example, on some makes you pull the latch back, on others you push it forward. Find out which feels most natural to HER.
The SP101 and the Smith J frames have small grips and may find them hard to control.
The Ruger GP series, Smith K & L series and Colt D and E series have larger grips.
The Smith N series and the Dan Wessons have large grips.
But more than anything, you need to find the gun, the grip and the caliber that SHE feels most comfortable with and shoots the best. Don't worry about the caliber. Even a 22 will take care of most situations and if she plunks a couple 22 or 25 rounds in the average home invader they will split posthaste.