IMO you are going about this the wrong way. There really isn't much difference in gun weight between a 20oz steel model 60 and a 15oz weight of your wife's 642. Look for a better set of grips for the 642. Practice with standard velocity or even lighter target wad cutters for shooting it. Load with defense ammo when carrying. No one pays any attention to recoil during a defense situation, if you are worrying about recoil you are really not in enough danger to be shooing someone.
To teach aim and trigger control get a .22 LR Ruger LCR or 2" S&W. This eliminates the recoil induced flinching for practice and this will carry through to all her shooting.
