Kids expend a lot of energy just being kids, and kids involved in sports expend even more.
Your granddaughter should eat a well-rounded diet with foods from all the basic food groups every day. Energy drinks and energy bars are fine, too. It's best to eat foods that are easy to digest - not too much fat or protein. Your granddaughter also should drink a lot of water before, during and after skating. I'll look for her in the Winter Olympics in a few years.