Let's start with the basics. Like a local NRA women only or NRA accredited one on one or class at the local gun store/range or shooting club.
This will immerse her into the shooting culture, expose here to many different firearms, and be in a relaxed atmosphere, introduce here to gun safety. Then when she has a good working knowledge of firearms,ammo, and how they work can she then make an informed choice. This will be her gun and here choice. No one else's.
www.corneredcat.com by Kathy Jackson is a good place to start as well. This site has info for women and men. Tells us guys a bunch about the women and shooting as well.
Your girlfriend may be at home right off with center-fire rounds like the .38 Special,9mm., or one of the .32 calibers. More on the .32 calibers later.
Who knows? A .45 ACP full size pistol might just be her cup of tea right off the bat.
The .22lrf pistol or revolver is a good way to go to start off with to get her used to handguns.
Low report, cheap practice, and non threatening with noise or recoil. The Ruger, Walther, Browning, etc., pistols would be good pistols to start with. Then go on from there.
Let's go up one step to the center fire rounds. The .32 calibers.
The .32 ACP in a Walther PPK/S, CZ83, Taurus PT132, or other quality pistol can fill the bill. The .32 ACP has the most of the same characteristics that the .22lrf cartridge has. Low recoil, low noise,and hits with more authority than the .22lrf out of short barrels.
Beretta, North American Arms, and others make pocket pistols for the .32 ACP.
Next up comes the .32 S&W Long, ,32 H&R magnum, .327 Federal magnum cartridges.Modern revolvers from S&W, Taurus, Ruger, and Charter Arms that can shoot all three or two of the three .32 cartridges. These hold 6 or 7 shots depending on the model.
These first two have the attributes that the .32 ACP has, but more power than the .32ACP. At least for the .32 H&R magnum.
The .327 Federal is in or a bit below the .357 magnum in power. If she can handle it, fine. If not she can stay with the .32 H&R magnum and the .32 S&W Long. The benefit is being able to tailor the ammo to the situation.
Next up is the .38 Special. It has the same attributes and advantages as the .32 calibers. Tailor the ammo to the situation. There are mild 130gr,132gr., or 148 gr. rounds for practice or for fun.
There are standard pressure and +P .38 Special rounds that will work for self defense.
9x17 or .380 ACP is up next. Beretta, Bersa, and others make mid frame .380ACP pistols. There are pocket pistols as well, but these have a bit more recoil and noise compared to the mid size framed guns. If she can handle it, no problem.
Last, but not least is the 9x19 Luger or Parabellum round. This cartridge has low recoil, low noise, and excellent defense capabilities. There are numerous excellent pistols out there. Most guns now come with adjustments for the hand-grips so it will fit any hand size.
There are the Beretta and Taurus pocket pistols, but that comes later.
I like both the Beretta 21A and the Taurus PT-22. I own 2 PT-22s, but like the Beretta 21A. Both have fine attributes. In the 1999 Complete Book of Auto Pistols, Gene Gangarosa wrote that the Taurus PT-22 and the Beretta were accuracy champs.
Depends on what the user finds easier to use. The Beretta has the traditional double action/single action trigger system,tip up barrel and a thumb safety. Holds 7 shots.
The Taurus is double action only, tip up barrel,and the thumb safety.Holds 8 shots.
It's also been observed by many gun writer/instructors that recent rimfire ammo in the last few years has had a very low rate of primer failures with premium .22lrf ammo. I have seen the same thing in my use of .22lrf ammo. It's comparable to centerfire ammo reliability. Not to say that the .25ACP should be passed up. Far from it.
The .25ACP crowd has a good point about centerfire ammo reliability.
Your girlfriend might even decide that the .45 ACP is the way to go.
Let her choose,try as many differerent calibers as possible, and let her make the choice as to what gun/caliber combo is right for her.