In 1947 after the Manhattan Project had been dismantled, Lathrop remained on staff at the lab as an associate biochemist as it was renamed Argonne National Laboratory. In 1954, tired of an exhausting commute, Lathrop left Argonne to pursue a career at the Argonne Cancer Research Hospital. It had opened in 1953 on the University of Chicago campus making it much closer to her home.
Lathrop was hired by the US Atomic Energy Commission facility as a research associate under the guidance of Paul Harper. Their goal was to find ways to manipulate radiation to allow for cancer detection and treatment. Their groundbreaking work on using the gamma camera to scan the body is a method still in practice to this day.
She published her last paper in 1999 and then retired in 2000.