Tsingou was born October 14, 1928, in Milwaukee to Greek immigrant parents. After limited teaching opportunities opened to women in mathematics, she joined the Los Alamos Scientific Laboratory in 1952 as a "human computer," one of the people who ran calculations by hand before electronic machines took over the work. She went on to earn a master's degree in mathematics from the University of Michigan in 1955 and spent nearly 40 years at Los Alamos, later contributing to thermonuclear research and the Strategic Defense Initiative.

Her defining work came in the 1950s, when she programmed the MANIAC I, an early electronic computer built from 3,000 vacuum tubes and weighing 1,000 pounds, to simulate a chain of particles connected by springs. The project, led by mathematician Stanislaw Ulam with physicists Enrico Fermi and John Pasta, set out to test how energy spreads through such a system. Tsingou wrote the code and ran the computations that produced the result: rather than dissolving into random disorder, the system settled into structured, recurring patterns. The finding became a foundation of nonlinear science and chaos theory.

When the work was published in 1955, Tsingou's name did not appear among the authors. A footnote thanked her for "efficient coding" and "running the computations." The study became known as the Fermi-Pasta-Ulam problem, and her role went largely unrecognized for more than 50 years.

That changed in 2008, when French physicist Thierry Dauxois published an article in Physics Today titled "Fermi, Pasta, Ulam, and a Mysterious Lady," documenting Tsingou's contribution. The episode is now widely known as the Fermi-Pasta-Ulam-Tsingou problem, or FPUT.

Asked about her role, Tsingou said simply: "I was just doing the job."

She is survived by her daughters, Ann Menzel and Carol Menzel, eight grandchildren and three great-grandchildren.