[1][2] Hornig was born in Ústí nad Labem in 1921[3] into a Jewish family[4] to Erwin Schwenk, an organic chemist, and the former Rascha Shapiro, a pediatrician.

After she was originally asked to take a typing test, her scientific skills were recognized and she was given a job as a staff scientist working with plutonium chemistry for the Manhattan Project.

While at Los Alamos, she signed a petition urging that the first atom bomb be used on an uninhabited island as a demonstration.

A feminist, Hornig was the founding director of HERS (Higher Education Resource Services) under the auspices of the Committee for the Concerns of Women in New England Colleges and Universities first organized by Sheila Tobias.

[11] In the 2023 film Oppenheimer, directed by Christopher Nolan, Hornig was portrayed by actor Olivia Thirlby.