Bustelo joined the
Spanish Socialist Workers' Party (PSOE) in 1974, after the Suresnes Congress. She lived in exile in Paris with her husband before returning to Spain in 1964, where she began clandestine political activity and feminist advocacy, collaborating with the Association of Housewives and the
Spanish Association of University Women. She co-founded the Federal Commission Women and Socialism with other PSOE feminists such as
Elena Arnedo in 1975, to propose gender equality policies within the party. Elected deputy for Madrid in the 1977 general election, she advocated for contraceptive legalization and constitutional equality. In 1979, she declined inclusion on PSOE electoral lists due to insufficient female representation. She served as the first director of the
Institute of Women (1983–1988) and was Undersecretary of the Ministry of Social Affairs from 1988 to 1990, resigning due to fatigue. == Women's rights advocacy ==