Michelle Trachtenberg has died at the age of 39. The actor, who was best known for her breakout role on Nickelodeon’s Harriet the Spy as well as later stints on Buffy the Vampire Slayer and Gossip Girl, was reportedly found dead Wednesday in her New York City apartment by her mother just after 8 a.m. local time.The news arrives after Trachtenberg underwent a liver transplant and may have been experiencing complications. In recent months, she had shared a series of troubling posts on Instagram in which she appeared extremely thin. She is believed to have died of natural causes and no foul play is suspected.Trachtenberg, who was born in New York, starred as a child in both Harriet and the Nickelodeon sitcom The Adventures of Pete & Pete. From 2000 to 2003 she played Dawn, the younger sister of Sarah Michelle Gellar’s Buffy on Buffy the Vampire Slayer. In 2021, she added her voice to those accusing that show’s creator, Joss Whedon, of inappropriate behavior. She said that he was not allowed to be in a room alone with her and called his behavior “Not. Appropriate.”