She died of a previously undiagnosed blood disorder, said her representative, Adam Kersh.
Her partner, the comedian and actor Marc Maron, said Shelton collapsed Friday after having been ill for a week. It was not Covid-19, he said.
“There was a previously unknown, underlying condition,” he said. “The doctors could not save her. They tried. Hard.”
Shelton began making films in her mid-30s, Kersh said, and went on to write and direct eight feature films in the span of 14 years. Among her films, she directed “Humpday” and “Your Sister’s Sister,” both starring Mark Duplass, as well as “Outside,” with Edie Falco.
“I’m so devastated to hear about Lynn Shelton’s passing,” Witherspoon tweeted. “I’m in complete shock that this vibrant, talented, and soulful filmmaker is no longer with us. Lynn was so passionate about our show.”
Duplass tweeted Shelton’s “boundless creative energy and infectious spirit were unrivaled. She made me better. We butted heads, made up, laughed, pushed each other. Like family. What a deep loss.”
Shelton was born in Ohio and grew up in Seattle, Kersh’s statement said, later moving to New York City.