Rose Farley fell ill at a birthday party on Friday evening and was taken to Alder Hey Children's Hospital where she died just after 5am yesterday.
A 16-year-old boy from Liverpool has been arrested by officers from Merseyside Police on suspicion of supplying drugs.
Miss Farley, from the West Derby area of the city, had been to the party but returned home after becoming ill before she was taken to hospital.
Her death comes amid reports her drinks may have been spiked at the party and just days after Merseyside Police warned youngsters of a deadly ecstasy-type drug circulating in the area.
A spokeswoman for the force said Miss Farley's death is still being treated as "unexplained" and although a post mortem examination had been carried out, the cause of her death has been withheld pending toxicology results.