Several years ago, the University of Michigan awarded the undergraduate Avery Hopward prise to Mildred Walker for a promising first novel, Fireweed. Now her third is the January choice of the Literary Guild -- unusual progress for a young writer. DR. NORTON'S WIFE is a psychological novel, with a medical background -- popular at the moment. Against a screen of a medical school with the members of the faculty and their wives, is played out the triangle drama of a member, his wife, who is a hopeless invalid, and her sister, a divorcee, living with them and keeping house in her sister's place. Sue is the focus of the story, and the tragedy of change in her relations with her husband and her the world around her is extremely well done. In the ultimate triumph of a best understanding and relationship, counterbalancing the attraction of health and love sympathy, one feels a wish to believe something that is made almost but not quite ineing. Easy reading, with promise of greater development.