Vinegar and the age-old (yuk!) peeing on your feet in the shower work to prevent fungus, but if there's peeling I agree with the last post-- use strong medication and go for the cream. Be patient too, I had the peeling athlete's foot once and a week of cream cleared it right up. My husband has success with the cream but it took more like 4-5 weeks and he has recurring bouts. He always keeps a tube in case his feet start to itch.
Tell your mom to use cotton socks as much as possible, remember to change socks often and wear flip-flops around places like public pools. Even something simple like panty hose can trap moisture and let fungus grow.