Christensen had been a staff editor at Grossett & Dunlap in the early 1980s, working on compilations such as The Illustrated Treasury of Humor for Children and The Platt & Munk Treasury of Stories for Children. She wrote the storybook Good Night, Little Kitten, Monsters: Creatures of Mystery, and a series of educational Snoopy books (Snoopy's ABCs, Snoopy's Book of Shapes, etc.) Her most recent book is Mouse at Night (2000).