I am a firm believer that ANY gun is better than no gun. I shun the idea of some people to insist on heavier calibers for recoil sensitive people. This always leads to them quitting or not using that weapon.
If 22mag is all she'll ever use, well that's fine. It will definately ruin someone's day or life. A headshot with that is fantastic - instant stopper. A semi-auto 22mag like a Ruger can deliver quite a few shots with zero muzzle rise in a short span of time. Any woman can spray down an attacker with 9 shots of 22mag all to the body in just seconds. There is no one who's going to eat that and keep coming for more.
Now, this isn't to say you shouldn't try something more powerful. An AR-15 with commercial loads and light bullets and a comp has virtually no recoil. 55 grain ammo at 2750fps doesn't kick much, it barely moves the rifle.
I've found the M1 carbine to kick more than some AR's. I don't have much experience with 9mm carbines - if they are even less than the 223 AR with commercial loads, go that route.
If 22mag is the only choice, don't worry. 1900fps in a lever action is nothing to sneaze at. People who bash it aren't exactly volunteering to stand infront of one. The best weapon will be the one she will practice with, the one she will enjoy.
When a woman enjoys a gun, she likes it. When she likes it, she trusts it. When she trusts it - she'll use it better. A body shot with 22mag is superior to a miss with an AK. Women, when they know a gun kicks or is too harsh for them, will always flinch or anticipate it going off. Accuracy dies, and with that goes any chance for scoring hits.