Georgina Bartter, of Longueville, was at the Harbourlife festival with friends when she reportedly collapsed after a suspected adverse reaction to drugs.
She was assessed at the scene by Ambulance paramedics before being taken to St Vincent’s Hospital, where she later died.
"The patron collapsed at 4.37pm and event security called event fist [sic] aid. A paramedic was there at 4.38, a second at 4.41 and NSW ambulance paramedics were with the patient at 4.45. She was taken to St Vincent's Hospital," the festival’s organisers said in a statement posted on the event's Facebook page.
"Right now our thoughts are with her family – we can hardly imagine the pain and heartbreak they must be feeling, and they have our deepest sympathy."
Her family said in a statement released to 9NEWS: "She was a beautiful and vibrant young woman, who was much loved and will be sadly missed. She had allergies, and it was extremely out of character."
Police arrested 78 people for drug offences during the dance party.
Inspector Stewart Leggat, of City Central police, urged people to report the sale of illegal synthetic substances because it could save a life.
"There's little to no quality control in the production of illicit drugs. Quite simply, you don't know what you are getting - seeking a synthetic high, could result in a serious injury or death," he said.
"If you know of a business or person who may be involved in the sale of illegal synthetic substances, please contact Crime Stoppers immediately. We don't need to know who you are; all we need is the information you have."
A report will be prepared for the Coroner outlining the circumstances surrounding the Ms Bartter's death.