the mites/lice have a 100% chance of killing the chick. the dust is unlikely to kill her! a little warm running water with some flea/tick shampoo will do her good. then after she is dry (with a blow drier preferably) sprinkle some dust on her and rub it in good. her chances are slim, but this is the best and only thing you can do. also wash and dust the mother an hour or so off her eggs wont hurt anything. do the chick FIRST and keep it seperate from the mother until the mother is clear of all lice and mites.