The woman suffered serious head injuries in an incident at a house in Glenmore Gardens.
The ambulance service was called at around 22:30 BST on Thursday.
A 22-year-old man was arrested on Friday morning but has since been released pending further enquiries.
A 27-year-old woman from Limavady is now in a critical condition in hospital following an attack in the County Londonderry town on Thursday night.