A buoyant, warm-hearted story with heroine to match as again this popular author touches upon a social ""problem"" -- in this case a community of Have-Nots. Hetty Beau, sixteen and fighting plumpness, was disenchanted by the first glimpse of the Grande Deluxe apartment house in Denver, where she moved with her parents. Not only were the apartments very down-at-the-heels, noisy, and full of people in the grip of poverty, but the only teen-agers were crippled Butch and shy Audrey, from a family of migratory workers and painfully grateful for a home no matter how shabby. It is Hetty, secure in family love, if not in money, who is responsible for helping Audrey adjust herself to her new life, for promoting a school election win with a slate of Have-Nots and minority teen-agers, and for bringing the Grande Deluxers together. Somehow it all makes sense, for Hetty is a vibrant delightful heroine- engaging always, even in her bouts with diets, poison ivy and the blues. The illustrations on green wash by Helen Blair are as appealing and lively as the text, although some may deplore the bilious cast.