Actress Michelle Trachtenberg, who brought both depth and range to roles on popular TV shows such as Gossip Girl and Buffy The Vampire Slayer, has died at age 39.

The New York Police Department responded to a 911 call around 8 a.m. in Manhattan Wednesday morning. “Upon arrival, officers observed a 39-year-old female unconscious and unresponsive,” and emergency medical services subsequently pronounced her deceased, police told NPR in a statement. The woman was identified as Trachtenberg. “Criminality is not suspected. The Medical Examiner will determine the cause of death. The investigation remains ongoing.”

A former child actress whose earliest credits included stints on soap opera and crime procedurals, Trachtenberg broke out at age 10 acting as the star of the 1996 movie Harriet the Spy.

“Miss Trachtenberg, who makes her screen debut as Harriet, gives a performance that is as endearing as it is devoid of self-conscious cuteness,” wrote New York Times critic Stephen Holden in his review. “Her Harriet is high-spirited and stubborn, but never unlikable.”

Trachtenberg brought similar buoyant qualities to her role as Dawn Summers, younger sister to Sarah Michelle Gellar’s Buffy in Buffy The Vampire Slayer. She joined the hit show in its fifth season, in 2000. In recent years, after cast members accused showrunner Joss Whedon of sexual impropriety and toxic bullying, she posted a statement on social media in support, saying that she had not been allowed to be in a room alone with him. (Whedon told New York Magazine that he had no idea about this rule.)

After Buffy ended in 2003, Trachtenberg worked steadily, with arcs on such television shows as Mercy and Weeds. In the peak Disney princess era, she starred in its 2005 film Ice Princess. But it was on Gossip Girl that Trachtenberg made the greatest impact on popular culture. She joined the CW show in 2008 as the devious Georgina Sparks. She was a fan favorite.

“A talent forever,” wrote one fan on a Reddit thread memorializing the young actress.