You could .223 for your young daughter all you want, but I wouldn't do it because it's not fair to the animal she wounds becuase she couldn't handel the recoil of a larger gun (not saying it will happen, but you're not stacking the odds in your favor, or the deers for that matter.) As others have stated yeah .223 can and does take down deer, but you leave yourself no margin for error. Obviously because your daughters younger just weighting up a .243win won't work either so that leaves you the option of braking it. As long as she was wearing ears even during the hunt I would be all for it and a .243 would give you an even better varmit rifle.