Officers and paramedics were called to Gainsborough House, Enfield, in the early hours of 21 August.
The woman was taken to an east London hospital where she later died.
A 24-year-old man was arrested by Met Police officers on suspicion of causing grievous bodily harm and later bailed pending further enquiries.
A post-mortem examination will be carried out in due course.
Detectives have asked for witnesses to come forward with more information.
The death of a woman in her 20s who is believed to have fallen from a fourth-floor flat in north London is being treated as "unexplained" by police.