If soft recoil characteristics are paramount, the Hornady 110 gr. FTX seems to be well regarded. The "old stalwart" 148 gr. wadcutter is also not a bad choice, but it's not a magic bullet by any stretch of the imagination either.

I can't say I've extensively fired Remington's LHP +P through snub nosed K-frames, but I can tell you from personal experience that it's a peach to shoot from 3" and 4" barrels, and I wouldn't say it's terribly unmanagable in an all steel J frame either. You might want to keep it in mind if your wife should become acclimated enough to handle the modest increase in felt recoil.

Ultimately, the "best" choice is what she can shoot the most accurately through her individual M10. I would recommend you try different loadings including the ones suggested by others (with the exception of overpriced "boutique" ammo like Buffalo Bore) and see which ones work best for her.