Who is Esperanza? Why is this so shocking to Matt? chapter 20

Esperanza Mendoza is Senator Mendoza's wife and the mother of Emilia and Maria. She disappeared when Maria was five, and Senator Mendoza and Emilia told Maria that Esperanza was dead. She actually left her family to fight against the evil of El Patron's opium empire and wrote "A History of Opium" which Matt reads and, realizing the author is Maria's mother, tells Maria the truth. At the Convent of Santa Clara, Esperanza defends the Lost Boys against the Keepers, and she sends Matt to Opium to investigate and end the lockdown. She promises to install Matt as the ruler of Opium with the backing of the U. S. and Atzlan governments if he will end the opium empire and open the border with Atzlan.