Did my niece deserve to be ed?

I am pro as long as it doesnt border abuse and I think your sister did the right thing. You cant comfort a child after they get ed or they wont learn if that is the way you choose to punish your kids. But its not really your place to step in to comfort her kids after something like that, she was right for telling you no because you would have been the rescuer and she would always run to you when she gets ed and thats wrong. Hope this helps.