From the horse's mouth

Diana G. Gallagher (born March 14, 1946) is an American author who writes books for children and young adults based on television series. She has contributed to book series based on Buffy the Vampire Slayer, Sabrina the Teenage Witch and Charmed, among others. Born in Paterson, New Jersey, she now lives in Florida with her husband, the writer Martin Burke. She sometimes also writes under the name Diana Burke. Gallagher won a Hugo Award for Best Fan Artist in 1988 under the name Diana Gallagher Wu.