What does a 50 cal. roundball weigh?

I think you can find a sabot load that will come real close, so recoil would be similar. Go with a lighter powder charge if need be, to reduce recoil. Let her practice with a lighter load, then if you think you need to, increase it for hunting. You probably won't need to adjust your sights/scope too much for hunting, but make sure they're still on. She won't feel that shot at game anyway.