twogood, you'll get more responses on this over in the Handgun forum.
However, while you're here, let me offer a few words of advice. First, spend a good deal of time reading various posts in this forum, as well as in Shotguns and Handguns - also, use the TFL Search feature. As a matter of fact, in some localities / situations the right rifle can be an excellent home defense firearm. Firearms are simply tools, and different types have different uses. You wouldn't want to use a screwdriver to hammer a nail, right?
So, for home defense, especially for your wife's use, you might want to investigate 20 gauge shotguns. Try various kinds - perhaps you have a friend or two with firearms?
Regarding something you can carry concealed when necessary, to some extent this depends on how you would have to carry - if you wear a coat all day you can conceal more than if you wear just golf shirts and slacks. Handguns are usually easy to rent at indoor ranges, and this is highly advisable - try before you buy whenever possible. And, keep researching to make the best possible choice for you - this is an important investment for you, and it should last a long, long time. Note that if you will have the gun in deep concealment it will be more likely to rust - stainless steel and polymer construction types are less likely to suffer.
For smaller semi-autos, many people like small Glocks, Kahr's and Kel-Tec's, in 9mm and .40 caliber. Many people also like revolvers for concealed carry, due to their simplicity and durability - Smith & Wesson and Ruger are common choices. Regarding reasonable stopping power, you'll see a lot of debate about this, and when you boil it all down it seems to result in: (1) shot placement is obviously the most important thing (so, you have to be able to hit what you're aiming at, no matter what firearm you buy), and (2) most people seem to feel that 9mm and .38 Special are the minimum calibers for stopping power - smaller certainly works, but generally is not advised.
You'll get a lot of different opinions over in Handguns, but try to begin narrowing down your questions.