As a young physics student in Budapest,[1] Klein was a member of a group of Hungarians including Paul Erdős, George Szekeres and Pál Turán that convened over interesting mathematical problems.
[1] Following the outbreak of World War II, Esther and George Szekeres emigrated to Australia after spending several years in Hongkew, a community of refugees located in Shanghai, China.
[3] In Australia, they originally shared an apartment in Adelaide with Márta Svéd, an old school friend of Szekeres, before moving to Sydney in 1964.
In Sydney, Esther lectured at Macquarie University and was actively involved in mathematics enrichment for high-school students.
[4] In 2004, she and George moved back to Adelaide, where, on 28 August 2005, she and her husband died within an hour of each other.