The daughter of Holby City star John Michie apparently took an “illegal substance” before her death at Bestival, her family said.
A statement to The Sun repeated that they did not believe there to have been “any malice” involved in her time at the festival.
The body of Louella Eve Fletcher-Michie was discovered in a wooded area on the edge of the festival site at Lulworth Castle, Dorset, on Monday.
Her family said their “hearts are broken by the horrific tragedy” and Ms Michie “(appears) to have taken an illegal substance”.
They added: “We would appreciate cautious and sensitive reporting until the facts are known.”
A man arrested on suspicion of murdering the 25-year-old and supplying a Class A drug has been released under investigation, police said last night.
A Dorset Police spokesman said: “An initial post-mortem examination took place on September 11, which showed no clear signs of an assault.
“However, further examinations will need to take place over the coming weeks, including toxicology, in order to establish if there are any substances in her system or other suspicious circumstances.
“A 28-year-old man, who was known to Louella, was arrested on suspicion of murder and supply of a controlled class A drug. He has now been released under investigation.”
A police spokeswoman declined to comment on which Class A drug the 28-year-old man had been arrested on suspicion of supplying.
Former Coronation Street actor Mr Michie, 66, previously told The Sun the family had lost their “angel” and described the death as “a tragic mistake, a tragic accident”.
“She touched so many lives. She was so very positive, so bright, so out there. She had such energy. The tributes to her have been incredible,” he told the newspaper.
In a statement, his agent said Mr Michie and wife Carol - a former Hot Gossip dancer - asked for privacy during the “traumatic time”.
On Monday, the organisers of Bestival said they were “devastated” by the death and were supporting police with the investigation.
The festival, organised by DJ Rob da Bank and his wife Josie, took place for the first time on the Lulworth Estate in Dorset this year. It was previously held on the Isle of Wight.
Acts including the XX, Dizzee Rascal, Rag ‘n’ Bone Man, Pet Shop Boys, Wiley and Laura Mvula performed at the four-day event.
Mr Michie, who currently plays neurosurgeon Guy Self in BBC medical drama Holby City, has two other children, Daisy and Sam.
He played Karl Munro in Coronation Street from 2011 to 2013, having starred as Detective Inspector Robbie Ross in drama series Taggart from 1998 to 2010.