Rachel Cosgrove

From Oz Wiki

Rachel Cosgrove (later Rachel Cosgrove Payes, 1922-1998) was one of the Royal Historians of Oz. She wrote The Hidden Valley of Oz, one of the last Oz books. Her follow-up book, The Wicked Witch of Oz was rejected by Reilly & Lee, but was eventually published by The International Wizard of Oz Club in 1993.