Vega,
If you have the money, and it ain't cheap, the single absolute best defensive pistol, according to every woman I know who's shot one, is HK's P7. The manual of arms is more intuitive to the uninitiated than any other gun. The P7, with a large grip, short slide, and unusual cocking mechanism, is the best thing going if the BG attempts a grab. For too many reasons to go into here, the P7 is easier to shoot well for beginning shooters--not to mention everyone else--than any other defensive handgun. It's more accurate than the vast majority of full size pistols, and yet is approximately the size of a PPK/S. It doesn't jam. Period. It has practically no recoil. If you want the best, I suggest you try to rent or borrow a P7 and have your wife shoot it. Both of you may wonder where this particular gun design has been all your lives. It's that good.