A longtime U.S. Postal worker was found dead in her truck on Friday after delivering mail when temperatures reached nearly 120 degrees in Southern California, her family said.

Peggy Frank, 63, was found unresponsive in her truck around 3 p.m. in Woodland Hills, FOX11 reported. Paramedics arrived at the scene and pronounced the grandmother dead after several attempts to revive her.

The exact cause of death was not released, but Frank’s family believes heat exhaustion may have led to her passing. Friday was Frank’s first day back on the job after she was placed on medical leave for a broken ankle, her family said.

Frank had been working for the U.S. Postal Service for 28 years.

"She loved what she did because she loved the people...I don't think they realize what kind of job that it is....it is not an easy job," Frank's sister, Lynn, told FOX11. "She was a type of person where she wanted to do it right and she wanted to do a good job.”

Robert Tipton, a neighbor of Frank, said the sweltering heat the day Frank died was like “a wall” hitting him. Temperatures hit 117 degrees in the Woodland Hills area on Friday.

"It was almost 120 degrees outside — when I came out it was just a wall of heat just hitting you," Tipton said. "It's one of the hottest days I've ever experienced out here in the valley.”

Frank reportedly had previous health issues. Her son said his mother suffered a heatstroke last May.

“Safety is our top priority for all our employees," a spokeswoman for the U.S. Postal Service told the Los Angeles Daily News in a statement. The Postal Service strives to ensure that they have the tools and training to do so safely.”

Frank’s sister said the U.S. Postal Service needs to change its system during hot days to prevent another death.

"I want them to realize what it's like and they need to do something," Lynn said.