I think the ideal would be a mid to large barrel (helps absorb recoil) with a small grip that she can get her hands around (and reach the trigger properly). If you get a 357 you can also shoot 38's from it and there's less recoil. Then if you want to carry, you can load it with the 357s.
When she is picking up guns in the store have her do this (I can't tell you how many people, especially women, mess this up):
Have her take a 1 handed grip, arm straight out, gun, wrist, elbow, shoulder all lined up. And have her see if she can press the trigger CORRECTLY. Keep an eye that she does not shift her grip. Doing this 1 handed she is less likely to move her grip. You would be amazed how many people will unconsciously move their strong hand to reach the trigger when using a 2 handed grip. This not only affects their aim but their ability to control the recoil. I have taught many women to shoot and this is the first step I have figured out to make sure they get a gun that fits THEM.