From an interview with Gregory Maguire, author of the 1995 novel Wicked, upon which the musical of the same name was based:
Q. What nonfictional character from history or modern culture would you like to re-imagine or reveal the secret history of?
A. My nonfictional heroines include Virginia Woolf, Emily Dickinson and Laura Nyro, who are all dead, sadly. In a way, Elphaba is based on all three of them.
UPDATE: More from Maguire on how he imagined Elphaba:
In her college years, I imagined her as [songwriter] Laura Nyro: long dark hair, beautiful voice and a lot of passion. Later on, I imagined her as young Virginia Woolf, who used to call her sister Vanessa “Nessa.” I was thinking of Edwardian young women not allowed into the same colleges as their boyfriends or brothers. In the second half of the story, when she goes to the castle and becomes a recluse, I thought of her as Emily Dickinson, who was so far ahead of her time, it took half a century to catch up to her. I liked that [Dickinson] had had the courage to withdraw from a community that was not healthy for her.
Kind of reminds me of the part of your book where Desmond Child mentions he based the female character in his “Livin’ La Vida Loca” on Laura. She keeps turning up in the weirdest places…