Rathbone was elected to Parliament in the 1929 general election, as an Independent MP. One of only fourteen women in the House of Commons, she used her new platform to extend her campaigning to feminist colonial issues, challenging child marriage and women's franchise inequalities in India and Palestine (then ruled under a British Mandate), and female circumcision (FGM) in Kenya. In 1933 she presciently warned of the danger posed by Hitler's regime, and henceforth foreign affairs became a priority. She was a member of the League of Nations Union, which involved her in investigative trips with other women MPs to eastern Europe and Spain, and in the rescue of child refugees from the Basque country.  She sent this letter on 'The Refugee Question at Santander' to William Wedgewood Benn MP in July 1937, asking for his support.