If the 642 is too light, and is thus challenging for her to deal with recoil, you might consider getting an all steel revolver, and perhaps switch to a six shooter for one extra round, like the new re-introduction of the Colt Cobra. Also, target wadcutters will cut way down on recoil, and are said to be pretty effective for self-defense due to flat meplat.
As of now she has no problem with the recoil.
