Born into a Jewish family in Russia in 1886, Kahan's family were forced to emigrate, and she moved to Britain at an early age. The Kahans lived at 6 Clapton Square in Hackney, London. She became an active socialist and joined the Social Democratic Federation (SDF). Within the SDF, she was a leading opponent of Ernest Belfort Bax's anti-feminism, and an ardent anti-militarist. After a resolution she proposed to the conference of the SDF's successor, the British Socialist Party, was approved against the wishes of the party leadership, she was elected to its executive. She worked alongside Theodore Rothstein in opposition to World War I, and supported the foundation of the Communist Party of Great Britain (CPGB).
Kahan married fellow communist William Peyton Coates (died 8 Aug 1963), and became known as Zelda Coates. Together, they set up the Anglo-Russian Parliamentary Committee. She co-wrote several books with her husband, including Soviets in Central Asia and Why Russia Will Win. The Coates lived at 37 Coolhurst Road, Hornsey, London N8 in later days.
- Henry Pelling, The British Communist Party: A Historical Profile
- Karen Hunt, Equivocal Feminists: The Social Democratic Federation and the Woman Question 1884-1911
- The Harvest in Russia: Cases of Starvation (Letters to the Editor), Manchester Guardian | Sep 13, 1933
- The Truth about Russia: Hunger in Spring, Plenty in Summer (Letters to the Editor), Manchester Guardian | Sep 20, 1933
- Andrew J. Williams, Labour and Russia: The Attitude of the Labour Party to the USSR, 1924-1934