the .257 roberts will have more recoil due to its heavier bullets, at the same velocity (or maybe they go a little faster, i cant remember). its not going to me a bone crusher in recoil, have her shoot something else you have thats bigger to have her see what recoil is like on those.
of course the 7mm-08 is never a bad option either.

propmahn
save the world, reload your brass