[2] Born in San José, Costa Rica, on 11 January 1902, Prieto spent her childhood on the Guarari farm in the hills of Las Hiras, Heredia.

She was herself an active feminist, a member of the Communist Party and the Costa Rican Women's Alliance (Alianza de Mujeres Costarricenses).

Attacking the conservative attitudes of the times, her drawing La perfecta casada (The Perfect Housewife) is a caricature of the image of a woman (Primera exposición centroamericana de artes plásticas, 1935.

As part of the women's pacifist movement after World War II Prieto worked toward promoting world peace, serving as a delegate at the Peace Conference of the Pacific Rim in Beijing for the Unión de Mujeres Costarricenses (Union of Costa Rican Women) which was led by Carmen Lyra.

[3] In 1974, Prieto released an album of collected folksongs on Indica Records and in 1976, she presented a series of essays in conferences accompanied by musician Juan F. Hernández.