Exiled for her communist activities after the Costa Rican Civil War, Castro later returned and founded several social welfare programs.

María Odilia Castro Hidalgo was born on 26 October 1908 in Santiago de Puriscal, Costa Rica.

Castro attended the Girls High School, worked with literacy and temperance campaigns, and participated in health seminars and summer camps for children of tubercular families.

She and fellow teachers María Alfaro de Mata, María Isabel Carvajal, Adela Ferreto, Angela García, Luisa González, Stella Peralta, Emilia Prieto, Lilia Ramos, Esther Silva and Hortensia Zelaya, who had been radicalized at the Normal School (teacher's college), challenged a society built on privilege and the roles of women being confined to home, marriage, and motherhood.

Castro was the founder and vice president of the Costa Rican Citizen Organization and the Federation of Voluntary Agencies.