Michelle Trachtenberg underwent a medical procedure before she died at age 39.

The Gossip Girl actress was found “unconscious and unresponsive” by police on the morning of Wednesday, Feb. 26. A cause of death has not been confirmed. However, Trachtenberg had recently undergone a liver transplant, sources tell PEOPLE.

Trachtenberg never publicly shared any health conditions. But in January 2024, she did respond to commenters on her Instagram when they suggested she was unwell after she shared a selfie to her grid.

“Fun fact. This is my face,” she captioned a follow-up post. “Not malnutrition no problems. Why do you have to hate? Get a calendar.”

Michelle Trachtenberg. Michelle Trachtenberg/Instagram

In a third post, she added, “I’ve received several comments recently about my appearance. I have never had plastic surgery I am happy and healthy. Check yourself haters.”

ABC News reported her liver transplant may have led to “complications.”

Kevin Winter/Getty

The NYPD previously confirmed to PEOPLE that officers responded to a 911 call at 1 Columbus Place in New York City, around 8:00 a.m., on Wednesday. “Upon arrival, officers observed a 39-year-old female unconscious and unresponsive,” the police said. “EMS responded to the location and pronounced the victim deceased. Criminality is not suspected.”

Sarah Michelle Gellar and Michelle Trachtenberg on ‘Buffy.’. Richard Cartwright/20th Century Fox/Courtesy Everett Collection

Trachtenberg began her career as a child actor starring in commercials before moving on to roles in Nickelodeon’s The Adventures of Pete & Pete and Harriet the Spy, as well as on All My Children. From there, she took on the role of Dawn Summers, Buffy’s little sister, in the cult classic series Buffy the Vampire Slayer.

After BTVS ended, Trachtenberg went on to play Georgina Sparks, a recurring character on Gossip Girl. She marked her final onscreen appearance in 2023 when she reprised the role of Georgina for two episodes of the Max reboot.