Amanda Bynes Demands Partygoer Deletes Her Pic During Surprise Appearance at NYLON's It Girl Prom

"She was very offbeat," a source tells E! News

Amanda Bynes didn't behave like a prom queen Monday night.

The former fashion student made a surprise appearance at NYLON magazine's It Girl Prom at New York City's Gilded Lily, E! News confirms. "Amanda was wearing sunglasses inside and kept changing from a jean jacket to a leather jacket," a partygoer says, noting that Bynes was often "walking back and forth." Bynes, 28, "was not drinking" and she hoped to keep a low profile. "One person went to take her picture and she ran up to them and said, 'You better delete that now,'" the source says. "She was very offbeat."

Bynes, who was with friends, did not interact with the party's performer, Charli XCX.

The former child star, known for her roles in Nickelodeon's All That and its spinoff, The Amanda Show, has been in the Big Apple since Friday, less than a week after she was arrested on suspicion of DUI. Bynes was charged with a misdemeanor Sept. 28, held on $15,000 bail and released later that day. While dining at Gladstone's restaurant at LAX Friday, a fellow flyer described her to E! News as "very coherent" while speaking to staff. Still, the flyer said Bynes seemed to be obsessed with her appearance. "She was talking to herself and putting on a ton of makeup," the traveler explained. "She would apply some, look in her compact and make weird pouty faces and they say to herself, 'Ok, that looks fine.'"

The What I Like About You star jetted to Manhattan, where she was photographed walking around the Upper East Side with a Band-Aid on her face. Bynes also rented Citi Bike and "appeared normal and stable," an eyewitness told E! News exclusively. "She looked great and was a good bike rider—nothing abnormal."

Bynes is currently on three years' probation stemming from her DUI arrest in 2012. In the summer of 2013, the She's the Man star was hospitalized after starting a small fire in a neighbor's driveway. The actress was subsequently placed under the care of her parents via a court-ordered conservatorship.

Bynes' conservatorship ended on Sept. 10. While Bynes was enrolled at L.A.'s Fashion Institute of Design & Merchandising in April, her mom assured that public the actress has "no mental illness whatsoever."

—Reporting by Jennifer Cooper