I carry mosue guns all the time. Understand, they are underpowere. It is a compromise.
ALL handguns are wee feeble little things compared to rifles. If I even had to defend my life I am going for my AR or a shotgun.
Much as I an not a fan of the man, Col Cooper was right, a rifle is for when you know there will be trouble, and handgun is when you think there might be trouble. At home, a longarm is a much better option.
But if it has to be a handgun, well, you want the biggest one you can shoot. I keep my 44 Mag by my bed loaded with 44 specials. Id hate to carry the damn thing, but it makes a fine house gun.
All things being equal, bigger is always better.
There is just no way to know what a person will do when they are shot. All the numbers and studies are worthless when it is your butt on the like.
Elmer Keith said a big bullet lets out more blood and in more air. The old farmbow from Idaho knew what he was talking about. When you want to stop someone, you need to get thier blood pressure to zero. If you blow a big hole in the circulatory system, or disrubt the nerves that control bloodflow, you have a better chance of getting the BP to Zero before he hurts you.
32 don't make big holes and they don't go deep enough to blow apart spines or brainstems (sorry to be graphic, but this is serious business.) so for defense it is a poor choice.
It is, however, better than your fingernails.
If your gf has her heart set on a certain gun, just buy it. If she like it she will practice with it and become a good shot. I would rather her have a 32 she can hit with than a 9mm she never practices with and can't shoot.
Happy shooting.
Joe