The 19-year-old died after being taken to Altnagelvin Hospital, and detectives are appealing for information to trace her last movements.
A man remains in custody in relation to her death.
The dead woman hasn't been named by police, but Detective Chief Inspector Michael Harvey, who is leading the enquiry has confirmed that she was 19, and from Co Down. She was in Derry as part of her university studies to become a nurse.
Shortly before 2.30 yesterday morning, paramedics were called to a flat at Cromore Gardens, where they found the woman unconscious at the foot of some stairs. She was taken to hospital, where she later died.
DCI Harvey says police know she was in a nightclub in the city centre with friends on Wednesday night, and they believe she left the nightclub in a taxi at about 1am.
He says police are keeping an open mind as to the circumstances of this death, adding that if anyone saw anything unusual in the Cromore Gardens area, they are asked to contact the detectives at Strand Road police station by calling the 101 non-emergency number and asking for extension 57072.
A 21-year-old man who was arrested yesterday remains in custody at the Antrim serious crime suite.