The girl has been in critical condition in hospital since the attack on April 1, when she was found near a parkade on Hargrave Street.
The decision to take the teen off life-support was made by family and chiefs, says a family member whom CBC is not identifying.
A 15-year-old boy was charged with aggravated assault and aggravated sexual assault the same day the girl was found. Those charges will likely be upgraded if she dies.
According to police, the boy and girl were both in care of the province's Child and Family Services system and were being housed at the same hotel not far from where the girl was found after the attack.
They had been walking around together downtown when some kind of argument erupted between them, police said at the time of the boy's arrest.
The boy had flagged down officers for help, claiming to have come across the injured girl. But after questioning him, police became suspicious of his story and pressed him further, which led to the arrest.