Her casket was brought into the St. Alexander Roman Catholic Church as the funeral service got underway at around 2 p.m. CT.
The funeral is taking place near Fontaine's home community of the Sagkeeng First Nation, which is located about 93 kilometres by road northeast of Winnipeg.
"She's been stolen from us," Robyn Fontaine, Tina's aunt, said before the service.
"She was just so outgoing and happy, and she had every intent of finishing school and getting her job, and she just wanted the best for her little sister and her brothers."
Fontaine's pallbearers, who include her brothers, cousins and uncles, have photographs of her on feathers made of burgundy-coloured felt, in a nod to Tina's favourite colour, the CBC's Jillian Taylor reported.
Fontaine's body was found Aug. 17 in a bag that was pulled out of the Red River near the Alexander Docks in Winnipeg.
Police are treating her death as a homicide. No arrests have been announced to date.
Earlier this week, investigators went door to door in the Winnipeg neighbourhood where Tina was last seen asking residents if they noticed anything suspicious recently.
The teen had been in foster care at the time she disappeared and was reported missing Aug. 9.
On Friday, members of Fontaine's family made offerings of tobacco around a sacred fire in a special ceremony to honour her.
The fire is meant to represent Tina's spirit, so she can be with her family as they say goodbye.