She was born Willo Davis in Grand Rapids, Michigan. In 1949, she married David W. Roberts. She was originally trained as a paramedic and began writing in her spare time. Her first book, "Murder At Grand Bay," (published in 1955) was written for an adult market. She won Edgar Allan Poe Awards ("Edgars") in 1989, 1995, and 1997 for best juvenile and best young adult mysteries. Her books included The View from the Cherry Tree, Twisted Summer, Sugar Isn't Everything, Don't Hurt Laurie, Megan's Island, Baby-Sitting Is a Dangerous Job, Hostage, The Girl with the Silver Eyes, The One Left Behind, Scared Stiff, Caught!, and Undercurrents.
Roberts died of congestive heart failure at the age of 76. According to publisher Simon & Schuster, "The One Left Behind would have been her hundredth book for children."