Kenneth Whitman--the defense attorney who lost the case of the first mother convicted of child abuse after her child's suicide--plans to write a book about the notorious trial and sell the movie rights to the book, the Fort Lauderdale (Fla.) News Sun-Sentinel reported Sunday. Whitman and his client, Theresa Jackson, had considered selling movie and book rights even before she was convicted Oct. 30 of three felonies in connection with the suicide of her 17-year-old daughter, Tina Mancini. Whitman, who is acting as Jackson's agent, said he hopes to select a producer for the sale of her television movie rights this month. Her sentencing is set Dec. 3 on charges of procuring sexual performances by a child, child abuse and forgery. He may be setting his sights--for $150,000 for TV movie rights--a little high, however; several unnamed producers quoted in the newspaper's story said $50,000 was a more typical figure.