A DAO or SA/DA revolver is the only way to go for a defensive .22 IMO, if you get a dud you just pull the trigger again.
Right, and it's not just the ammo that can be less reliable than what you'd want in a carry weapon (although there are a few rather reliable brands), as .22 LR autoloaders generally tend to be less reliable in my experience (probably has to do with the low recoil and rimmed cartridge).
The Smith & Wesson 317 revolver holds 8 rounds and is sized well for carry--this would be my personal recommendation, for what it's worth. Get the one with the 3" barrel if that's feasible because for defensive purposes you'll want all the power you can squeeze out of this small caliber. The ammo that I would recommend for personal defense is the CCI Velocitor. Use any cheap ammo you like for general target practice, although I'd avoid Remington rimfire ammo altogether.
why a 22? i think you're underestimating her. we men tend to think women will be recoil sensitive -- sure, some are, but a lot aren't. my wife is little, but any cartridge i find comfortable to shoot, she finds comfortable to shoot.
I think that most men are recoil-sensitive, too, and could probably shoot .22 LR significantly better than more powerful calibers unless they train quite a bit. My 4'11" mom can slow-fire even Magnum calibers accurately, but she can shoot .22 LR a whole lot faster with good accuracy (all hits in the COM at 7-10 yards), so she currently uses a .22 LR for personal defense. Maybe she'll move up in caliber someday when she's more comfortable with recoil, and in that case the great thing about .22 LR guns is that everybody should have at least one anyway, even if you no longer intend to use it defensively.
Obviously, each person is different, so everybody should be allowed to find through experimentation what they're personally comfortable with. All I'm saying is that defensive shooting is different from simply being able to shoot one round at a time at a harmless, stationary paper target, and that .22 LR generally makes beginners better shots, which is a good thing for carry weapons despite the relative weakness of the caliber.
a much bigger concern for most women than recoil, i think, is the diameter of a gun's grip and the distance to the trigger. this is where my wife will have issues because her hands are small.
That along with the weight of the trigger pull, which can be rather heavy with some revolvers in DA mode. The OP should find out whether these potential issues apply in this case, and then we can address them.