[1] Rivera was one of the first members of the Pro-Emancipation Movement of Chilean Women (MEMCH) which was begun on 11 May 1935 by Elena Caffarena, who invited fellow "adventurers" to join in her feminist ideal.

Besides Rivera, who was listed as "doctora" were: attorney, Flora Heredia; Chief Inspector and director of women workers, Clara Williams; journalist, Marta Vergara; professors, Aída Parada, Domitila Ulloa and Susana Depassier; trade union organizers, Eulogia Román and María Ramírez; Angelina Matte;[2] Graciela Mandujano;[3] Felisa Vergara;[2] Olga Poblete[3] and Herta Hoschhauser, Elena’s best friend.

In addition, they recommended a broad education program so that all members of society, including children and the elderly understood both the benefits and dangers of nuclear power.

[7] On 8 January 1949 when the president of Chile finally signed into law the bill giving women the right to vote, none of the feminists who had worked for suffrage were allowed to attend the ceremony.

They listened at home on their radios as the names of the legislators and the feminists who had fought for 35 years were read..."Amanda Labarca, Elcira Vergara, Marta Correa, Maria de Hidalgo, Felisa Vergara, María de Arancibia Laso, Elena Caffarena, Raquel García, Flor Heredia, Aída Yávar, María Rivera, Magaly Negroni, Marta Ossa, María Aguirre, Marta Vergara, Graciela Lacoste, Graciela Mandujano ...".