Rinelle Harper is still in intensive care after she was sexually assaulted Friday, left with severe injuries on a walkway near the Assiniboine River, and found by a passer-by on Saturday morning.
Homicide investigators were called in because she wasn't expected to survive.
With her family's permission, Winnipeg police identified her in hopes of solving the case.
But the girl's uncle, Bruce Harper, said late Tuesday night, said the family never gave anyone permission to hold a rally in her name.
The poster for the event, which is called 'Justice for Rinelle Harper' and features a photo of the teen, says the rally is being organized by 'missing and murdered indigineous woman' (sic).
Harper said the family has not agreed to it at all.
"We were never notified or even asked for an image of Rinelle to be used on a poster or on a website," he said.
"She's not missing and she's not murdered. I do understand the situation and emotion involved and the importance of the [missing and murdered women] movement. But there should be some communication involved in situations like this."
Harper said Rinelle herself doesn't know about the rally. He said she is still 'a bit distraught' after the attack, in intensive care and very tired.
CBC wasn't able to contact the organizers of the event.