Illustration: Hokyoung Kim for HuffPost

When Peggy Frank returned to her mail route following three months of medical leave, Los Angeles was in the middle of a scorching heat wave .

The 63-year-old letter carrier had slipped on a patch of wet leaves and broken her ankle in March, and she spent the spring at home in a walking boot. Although the injury still bothered her, Frank had been cleared to go back to work. She was just two years away from retirement when she climbed back into her U.S. Postal Service truck on July 6, 2018.

The temperature had topped out in the high 80s in the first days of the month, but then it shot up dramatically after the July 4 holiday, putting Southern California under an extreme heat advisory. On July 5, the highs surpassed 100 degrees.

Franks sister, Lynn Calkins, had warned her to be safe as she prepared for her first day back. I said, Youre not used to it. Just be careful, Calkins recalled.

The two shared a townhouse in the North Hills neighborhood, and Calkins always made sure the ice trays were filled the evening before a hot day so Frank could load up her water jug before heading out at 7:30 a.m.

Getting an early start on her Woodland Hills route only helped so much it was closing in on 100 degrees in downtown Los Angeles by late morning. By the afternoon, the weather stations in nearby Burbank and Van Nuys, in Los Angeles San Fernando Valley, hit 114 and 117, respectively the hottest temperatures ever recorded there.