A widow with five children in her late 30s, she became a perennial best-seller over the second half of her life, writing or co-writing “A Stranger Is Watching,” “Daddy’s Little Girl” and more than 50 other favorites. Sales topped 100 million copies and honors came from all over, whether a Chevalier of the Order of Arts and Letters in France or a “Grand Master” statuette back home from the Mystery Writers of America. Many of her books, including “A Stranger is Watching” and “Lucky Day,” were adapted for movies and television. She also collaborated on several novels with her daughter,...