Glock 19 -9mm not too small and easy to handle, Never jams, always shoots, holds 15 rounds per clipand requires almost zero maintenance

I own a lot of handguns but this was my first and still sits on my nightstand on top of my bible.

Any of the above referenced handguns will suffice. But you should BOTH go to the gun shop and decide together. You don't want something too big for her hand and/or too small for yous.
But for strictly home defense, I would have to agree with stalkingbear's suggestion of a short barreled 20 gauge pump shotgun. Loaded with #4 or #6 and an open choke it will definately stop a home invader in his tracks. And it would be much easier to hit him with at night. And even if she ran out of shells, it would still make a handy club to beat the crap out of him.

Shotguns are the ideal home defense/protection weapon. Any of the pistols mentioned have the drawback of possibly penetrating an interior wall and killing an unintended target. This is not the case with a shotgun. You don't have to worry about accuracy in a stressful situation. Finally, the pumpshotgun has one more advantage over a pistol, the sound of chambering a shell. Nothing else sounds like that. If I had broken into a house and heard that sound from down the hall, I would be getting out fast.

Well, my first 4 choices would be:
1) S&W J frame 4" in 38 spl
2) Kahr 9mm
3) Glock 19 9mm
4) Springfield XD 9

Let grip fitr to her hand and trigger reach be the deciding factor. Then look for maintenance insensitive guns like the Glock 19 or XD-9. Avoid short barrels and poor balance when loaded. The XD and G 19 will feel unbalanced w/o ammo in them. They should be ok loaded.

My preferences are with well made 1911 handguns in .45 auto.
People grip handguns differently due to their physiology, A 1911 just points perfectly for me where other guns don't quite as well for me.

As others mentioned shotgun>pistol.

I'd like to offer another perspective- a carbine. Carbines typically have a lot more power than a pistol, are much easier to aim, and don't have the recoil of a shotgun. A m1 carbine is very light and handy and packs a good punch. A ruger mini-14 or deerfield carbine even more so. Beretta, Kel-tec, and highpoint make somenice little pistol carbines in 9mm and .40 S&W. An ar-15 carbine offers a great deal of versatility if you wanted to add a light, night sights, lazers, etc.