Seven-year-old Katelynn Sampson died in 2008 with 70 injuries found on her body, in a case that drew outrage.
Police say Warren Johnson, 50, and Donna Irving, 33, beat the girl for months until she went into septic shock.
It was later revealed a family court judge had granted custody of the child to Irving, despite her criminal convictions for prostitution, drugs and violence.
Advocates at the time argued that a number of points of protection had failed Katelynn.
The province has since made changes requiring guardians applying for custody who are not parents to provide a police background check as part of their application.
The pair took Katelynn into their home when her drug-addicted mother tried to get clean and promised to pay them $200 a month.
"I am in pain, I'm hurt all the time, I have a constant sense of hopelessness," Katelynn's mother Bernice said in a victim impact statement. "All I want to know is why, why did they take something that didn't belong to them?"
Katelynn's grandmother also read a statement, along with a former teacher and the principal at her former school.