German stepdaughter and full-time secretary of Albert Einstein who helped to collect and preserve Einstein’s written legacy.
Ilse’s father was Elsa’s first husband, textile trader Max Löwenthal (1864–1914). Max and Elsa Löwenthal had two daughters, Ilse and Margot (1899-1986), and a son born in 1903, who died shortly after birth. They divorced on 11 May 1908, and Elsa moved with her two daughters to an apartment above her parents’ residence in Berlin.
Elsa began a relationship with her cousin Albert Einstein in April 1912, while Albert was still married to his first wife, the physicist Mileva Mari?. Einstein separated from Mileva in 1914 and their divorce was final on 14 February 1919. Elsa married him three and a half months later, on 2 June 1919.
Elsa’s and Albert’s mothers were sisters, which made Elsa and Albert maternal first cousins, and their fathers were first cousins.
With stepdaughters Ilse and Margot, the Einsteins formed a close-knit family. Although Albert and Elsa did not have any children of their own, Albert raised Ilse and Margot as his own. They lived in the Berlin area, also having a summer house in Caputh in nearby Potsdam.
Ilse Einstein had a romantic relationship with psychologist Georg Friedrich Nicolai (1874-1964) before she married literary journalist Rudolf Kayser (1889–1964) in 1924. Kayser, under the pen name Anton Reiser, wrote one of the first biographies of Einstein, published in 1930.
In 1933, Albert and Elsa Einstein emigrated to Princeton, New Jersey, USA. Shortly afterwards, Elsa travelled to Paris because Ilse was terminally ill with leukaemia. Ilse and her husband lived there with Margot. Ilse died in 1934.
Her mother Elsa Einstein died after a painful illness on 20 December 1936.

Link to Elsa Einstein: Married life