Of course it's all about shot placement as well, but the fact is that very few people even consider shot placement in a self defense situation. They're going to draw and fire wherever they can. So, while she might get a lucky hit with a .22, you're taking an extreme chance at using it as a self defense weapon. I've seen people take multiple hits from a .223 round, which is much much larger, and still keep coming.
As for the legality of her carrying, she's fine. She could even purchase a firearm from a private party as long as your sheriff isn't retarded and knows the laws.