A 62-year-old animal activist was charged in connection with an undercover operation intended to expose conditions inside a San Joaquin County cage-free egg-supplier.

In one of a series of nighttime visits to Pleasant Valley Farms, a supplier of eggs to Costco located in Farmington, Redwood City resident Diane Gandee Sorbi removed from the facility an injured hen that couldn’t walk, according to Direct Action Everywhere, the animal activist organization that recorded undercover video at the farm.

Sorbi was charged with theft, larceny and criminal mischief, according to a letter from the district attorney’s office. She was not arrested, but must appear in court Feb. 10, the letter states.

Inside the barn, video shows a number of dead birds — and others the activists said were sick — as well as hens with injuries from other hens.

A lawyer for Sorbi, Sonya Mehta of the Siegel & Yee law firm, said in a statement her client was “helping animals who were sick and suffering.”

The removed hen, which activists named Ella, was “dying and would have literally been thrown into the garbage by the farm,” Mehta said.

“Instead, she is now healthy and living at a sanctuary — which is what every animal deserves,” Mehta said.

After the footage came to light, Pleasant Valley Farms released a statement categorizing the group’s action as trespassing and claimed the video was staged for “production effect,” the New York Times reported.

Mehta said Sorbi planned to plea not guilty.

Michael Bodley is a San Francisco Chronicle staff writer. Email: mbodley@sfchronicle.com. Twitter: @michael_bodley