The hardest-working woman in show business right now seems to be the entrancing, ubiquitous Samantha Mathis. Movie critics developed crushes on her in the recent Christian Slater film Pump Up the Volume, and in the past two months she's illuminated no fewer than three TV movies: She was the spunky girl in Extreme Close-Up, the spunky-girl-buried-underground in 83 Hours 'Til Dawn, and now she's the spunky daughter in To My Daughter (CBS, Mon., Nov. 26, 9-11 p.m.).
The movie itself is weepy junk: Rue McClanahan (The Golden Girls) plays a prim matriarch who has love only for her oldest daughter, Michele Greene (L.A. Law). Mathis has a smaller role as the neglected girl in the family, but once again, she is spunk transcendent. Her flat, wide face isn't conventionally pretty, and hooray for that: Freed from the obligations of bimbo-dom, Mathis conveys intelligence and mysteriousness behind her sparkly eyes and slow, sexy smile you always want to ask her, ''What are you thinking about?'' Here's hoping that scads of Hollywood producers are thinking up good TV shows and movies to put her in.