He's got a point. Rare would be the fail to fire (but of course the hammer will drop on a loaded chamber if it's on safe, an easy mistake to make). Much more likely is the FTE. Which honestly is a concern given the stopping power of .22lr. That said, I've never had any cycling troubles with mini mags (or really anything else for that matter...my P22 has overall been pretty reliable).
Make sure mini mags run through fine, keep the gun clean, make sure she's aware that she'd have to work the safety (or keep it in an accessible, quick-draw holster, safety off, hammer up), and I think the P22 could be a sufficient self-defense tool.
Granted, I would not fight a war with it, but the gun alone will act as a deterrent. If necessary you know it will cycle 10+1 rounds of mini mags or whatever you choose.
Once you've finished paying for the ring, wedding, honeymoon, furniture, house, and all the other s*&% women want, get a more reliable piece for her and use the P22 as a suppressor host!