I'm going to disagree with some of the thoughts on here.
As far as "fitting her hand", we're not talking a shotgun here. It's a handgun, fit is not that big of an issue. I train people to use handguns. By and large, the number one issue women have with handguns is that they are too big. So, bottom line is don't buy her a Glock 21 and think all is well. She should be able to shoot it fine, and many women can. However, they run into the issue of the grip size being too big and they cannot get enough of their trigger finger on the trigger to shoot it comfortably.
That said, a Glock 17, or any subcompact 9mm is going to be just fine as far as grip size. Grip ergonomics can easily be overthought also. She's not shooting a competition, she just needs to be able to grip the gun and press the trigger.
Revolvers are fine, but I don't really agree that a revolver is all that much more simple relative to today's semi auto pistols. A Glock or a Springfield XDS does not have a manual/external safety, and can be fired if the magazine is disengaged. They are very foolproof, hence the reason many cops use and carry them. Also, a Glock is going to have a nicer trigger pull relative to many of the more inexpensive revolvers.
Revolvers MAY be somewhat more reliable. All things considered, if you take reloads out of the equation (speed reloads with pistol will be much easier than revolver), there are pros and cons to each that when weighed out don't really amount to a very negligible difference.
Shooting a pistol is not as difficult as we make it out to be. Learn a proper grip, learn proper sight alignment, and learn a proper trigger press. If she is merely carrying it for protection then that's not really a high bar to clear.
Good luck!
