I hate to be critical of you also but if she is shooting 4" groups at 100 yards then no way would I let her take a 200+ yard shot on an animal. You said he was "floppinf" around. She probably shot it in the front leg and broke it out from underneath him.

The .243 is more than enough cartridge for any deer alive. It's not the cartridge.

Bottom line is that you need to have her practice a lot more and until she can consistantly make long shots on paper limit her shots to less than 100 yards.