I would like to share with you my personal experience. My wife never even shot a gun before she met me. We got married and I just started her out on my ruger mk 2 22lr just plinking. didn't even talk about sights and the use of them. just trying to sneak in a "love for shooting 22s" she quickly went thru about 1500 rounds of 22 lr over the course of a few months and year or so. She quickly learned sighted/unsighted shooting. every once in a while she would shoot my glock 19 9mm. Slowly and up to present, shooting a 9mm is fine with her.
Please try to make shooting fun first of all, and then she'll keep doing it.
YOU may find that as your wife shoots lots of 22, then other larger, more adequate home protection rounds aren't that big of a deal for your wife to shoot. That's when she will see for herself that a nine or a 40 is a safer bet than a 22 for HD
I think that women aren't so much afraid of recoil and noise exclusively, but the whole cloth of the "newness of the experience of shooting". Once that wears off, then shooting bigger guns is fine, because now they are comfortable with loading, unloading, aiming, shooting, safe handling practices, etc.
That said, then if she wants to only shoot 22s for HD, then consider a revolver 22. if a 22 squibs out, pull the trigger again. Cylinder rotates, yer back in business.
For those who crap their pants when thinking about 22 for home defense, then consider the idea that if any of us had the luxury of choosing what to use for a lethal force encounter, only the dimmest dullards would choose a handgun of any caliber. 22 lr is more than fine for HD, but there are better choices. Another tiny choice is the 32 H&H mag. Sweeeeet.
Above all, try to foster regular shooting sessions, no matter what she and you choose-caliber wise. You know, like a date night. Happy shooting.
john l