On the maternal side, she was the niece of doctor and politician Manuel J. Barrenechea Naranjo [es], and was also the cousin of the father of writer and politician Julio Barrenechea.
[1] Contreras was a member of the Socialist Party of Chile (PS) since its founding in 1933, specializing in the area of Social Women's Action.
[1] Contreras was appointed mayor of the commune of Santiago by President Pedro Aguirre Cerda, her nomination being supported by the Pro-Emancipation Movement of Chilean Women (MEMCH),[1] a position she assumed on 6 January 1939.
[3] With this, she became the first mayor of Santiago[4] – after her, only three women have held that position: María Teresa del Canto (1953–1957), María Eugenia Oyarzún (1975–1976), and Carolina Tohá (2012–2016).
[3] During her term she coordinated relief efforts after the Chillán earthquake,[7] expanded playgrounds and sports programs in working-class neighborhoods,[8] opened a hostel for shoeshiners,[9] and was a delegate to the Inter-American Commission of Women, working to increase civil and political rights for women.