Derek Nepinak, chief of the Assembly of Manitoba Chiefs, says the girl's family gathered at the hospital and made the agonizing decision Wednesday.
He says the family was at her bedside and has asked for privacy.
The girl was beaten and left for dead at a parkade in downtown Winnipeg on April 1.
Police charged a 15-year-old boy with aggravated assault and aggravated sexual assault.
Both teens were in foster care and were being housed in the same downtown hotel.
"They are at her bedside now in a heartbreaking situation," Nepinak said Wednesday night.
The attack prompted Manitoba Family Services Minister Kerri Irvin-Ross to promise to stop housing foster children in hotels by June 1.
Manitoba has about 10,000 children in care. The vast majority are aboriginal. On any given day, dozens of those children are put up in hotels because there isn't room in a foster or group home.
The provincial government has been under fire for housing foster children in hotels for 15 years.
Manitoba's Children's Advocate has released several critical reports about the practice since 2000, urging the government to find better alternatives.
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