My personal opinion and experiences with my wife, would lead me to suggest a revolver. Now, it's not "Sheik" like most people would prefer, but it is probably more effective and infallible under duress, for a woman without significant combat training. Sometimes under stress, a semi auto pistol may have too many "bells & whistles" for those without proper training. If it must be a semi auto pistol, make sure you choose a proven and reliable gun. I'd suggest something in a SA only design, without too much complication from an external, manual safety. Cheap semi autos are about useless, and are prone to stove piping and feeding problems, even from something as simple as shooting the gun cocked a little sideways. Cheap guns are finnicky about ammo, and cannot be relied upon at the range, let alone in a life and death situation.
As for particular guns, there are MANY options. My personal preference in a revolver for my wife, would be a J frame. In a semi auto for most females, I'd opt for a Springfield XD 9mm sub compact, or a sub compact Glock in 9mm. I think today's 9mm is a much more viable self defense round, as compared to the offerings of even 10 years ago. They are now loaded hotter, and in more configurations. You could also go 380 ACP, but for what ever reasons, I'm just not a fan of the caliber and choices of guns in that caliber. For myself, I'd rather carry a snubbie loaded with 38 +P ammo. Regardless of what you settle on, situational practice and functional knowledge of the firearm is the real key. You are ALWAYS going to be more effective with a gun that you have confidence in, and shoot well, regardless of caliber. Good luck!
