Usually, the behavior involves vainity or youth obsession. Many also have this disorder out compulsiveness. Usually she will spend time making fatty concoctions to force feed her family (eating fatty grandma type cuisine vicariously through others), but she won't eat any of it more than once every 3 days. She always refuses to go to restaurants, claiming to hate them or that she thinks they are unclean. The reality is because the temptation is too great.
You take your child to see grandma, and she looks all skeletal and haggard, with clothing from "forever 21, " and you start to become concerned that granny is a "granorexic"