How long does it take for a salt and ice burn to go away? Is there anyway to treat it?

My friend is 13, and her cousin told her to put salt on her hand, and then ice. She didn't know about what would happen and that she would get frost bite from it. Anyway, she's really worried and wants the burn to go away. She got the frostbite/burn about a week ago, and is worried it's going to be a scar. Is there anyway to treat it? And how long will it take to go away? She's really worried, and I told her I would ask.