I agree with Paige, I've never had to put a cone on any of my boys after neutering, and it probably just adds to the alienation from his sister. I am guessing she is freaked out by the cone and the smell from the hospital. I would try just the opposite of what was suggested - rub her down with a towel and then rub him with it so that you get her scent onto him. Eventually the weird smells will go away and she will be accepting again, but it can sometimes take a few days.