This subject should be approached from a self-defense perspective rather than of one as a shooter. They are two very different pursuits. If your wife knows absolutely nothing about personal defense or using firearms in that context, she would not be very helpful in determining what an effective weapon choice would be even for herself and likely pick based on appearance and comfort. She has to be able to effectively grip the pistol(not the same thing as being comfortable in the hand) and be able to reach and work the trigger.
Civilian defense encounters happen at extreme close quarters. She needs to be able to make multiple combat accurate hits at close range in fairly quick succession. She should be able to shoot it one handed, from retention as well as from unorthodox positions, which is the norm in civilian self-defense. Limp-wristing is a HUGE issue with small semi-automatics in this context. I've seen numerous people(especially women) who can shot an auto just fine from a established stance either a two handed grip, but have them fire it one handed from relaxed stance or while moving, and they will often have malfunctions. This is not an issue with a revolver. A short barreled, lightweight j-frame, particularly with an enclosed hammer is something she'll likely keep handy(ideally on her person)at all times(there may not be time or opportunity to retrieve it), it offers excellent weapon retention and has many close quarter advantages.
Violent criminals want to catch you off-guard and unprepared. Folks need to get out of this mindset that they are always going to have substantial warning, lead time and distance to retrieve firearms or will have time to take up a position, lie in wait, take a range stance, readying self to fire with a picture perfect grip while someone kicks in their door. That can and does sometimes happen, but it just as often does not and it's those ambush/counter-ambush scenarios that we are most worried about.
Generally, the more training the better, but really not a necessity. She doesn't need to shoot a whole lot or go to the range frequently to be able to learn and use a firearm effective. Simply putting a lot of rounds down range from a static stance using a perfect two handed grip isn't very effective training for the realities of a home invasion.
If she can effectively shoot the firearm, recoil shouldn't really be much of a concern, even if it makes her want to limit her live fire training. A substantial defense caliber like a .38 special she is efficient enough with even if she doesn't really enjoy shooting is still better than a sub-caliber like .22 that she loves to shoot and practices with often when it comes to self-defense. Refusing or being scared to shoot at all though would be a very big problem. Self-defense is the goal, not simply being a shooter.
A woman home alone(or just her and children)is a very different scenario than when is there is an adult male in the home and intruders will often approach it differently. Woman are by nature, more trusting, less environmentally aware of violent threats and generally react and respond less favorably and effectively in violent crisis. He(they) will often be more aggressive and less easily deterred by expectations or threats of resistance, because that is what he has learned through his life as a predator and what is often reality. To best address the situation, you must learn these lessons as well to understand how best to defend against them.
Having a gun is just part of the total equation. You have to have a well rehearsed plan and a working knowledge of how actual scenarios unfold and where you're vulnerable. Answering the door, taking out the trash, letting the dog or cat outside, getting the mail, coming home through the front door or even the garage are opportunities criminals take advantage of most people never think about.
Here's a compilation of video footage of various home invasions that are worthy of study.
http://wilsondefense.blogspot.com/2015/08/home-invasions-caught-on-camera.html
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