As a peace activist, she was involved in the promotion of pacifism and believing women had unique qualities for solving world problems, she established the International Scientific Institute for Feminine Interpretation.

In 1982, in recognition of her significant contributions to the Dutch Women's Movement, Posthumus-van der Goot was appointed as an officer in the Order of Orange-Nassau.

[4][3] Soon after completing her studies, on 19 January 1931 in London, Van der Goot married Nicolaas Wilhelmus Posthumus, a professor of economic history whom she had met during her schooling.

[1] In trying to prepare the report, Posthumus-van der Goot recognized that there were no archival records which could be consulted that dealt solely with women's history.

[5] That same year, she also became involved in pacifism and attended the Universal Gathering of Peace (French: Rassemblement universel pour la paix), held in Brussels.

When German soldiers were billeted in their home, the household moved to Leiden and began to work with the Dutch resistance to smuggle children out of Amsterdam and place them with foster families.

[4] In 1940, the majority of the IAV collections were confiscated by Nazi looters and Rosa Manus was arrested, deported to a concentration camp and murdered.

[5] The following year, Johanna Naber also died,[6] leaving Posthumus-van der Goot as the sole living founder of the IAV and in charge of recovery attempts.

[2] That same year, Posthumus-van der Goot began working with Jane de Iongh [nl] and Marga Klompé on reorganizing the IAV for the post-war period.

[5] The office gave assistance to women in a wide-ranging platform focusing on topics from household chores to make-up and published a newsletter, with tips and advice until 1964.

[1] She served as chair in 1964, of the Dutch women's committee to prepare for the Year International Cooperation recognized by the United Nations in 1965.