In infancy, daughter Catherine wailed incessantly and flopped like a doll. At eight months the official diagnosis was sobering: severe retardation and cerebral palsy. But mother Nicola resolved to keep Catherine at home in Winnipeg and live a normal family life; more than fifteen years later, Cath has her own bedroom and special equipment and two devoted younger brothers--evidence of her mother's imperturbability and her father's less generous presence. As a youngster, she was so vacant, so frequently in a ""turned off"" position, that a genuinely puzzled nine-year-old asked the title question; but slowly Cath did respond to the people around her, to particular stimulations or the advent of a thoughtfully designed chair, and that same observer could comment, ""It's sad, but she isn't."" More problematic is her future disposition. The only available institution is so wretchedly inadequate that Nicola joined with the parents of other multiply handicapped children to petition for a better facility--one of those well-wrought proposals, involving hours of volunteer work, that eventually succumbed to government indifference. Readers will share Cath's few triumphs and admire Nicola--she's got more spunk than nobility and she never preaches.