Lulonda Flett, 41, had pleaded guilty to manslaughter and arson for a deadly blaze that was prompted by anger at her boyfriend's mother.
"One cannot overstate the gravity of these offences," Court of Queen's Bench Justice Deborah McCawley said Thursday.
She called the crime a "selfish, deliberate and reckless act."
Court was told Flett was on probation in July 2011 and had just been released from jail three days earlier for assaulting her boyfriend. She decided to take revenge and set fire to a couch on the porch of the two-storey Winnipeg rooming house where her boyfriend's mother lived, because the mother had called police about the assault.
The fire spread quickly, killing five people inside and injuring others. Her boyfriend's mother was among those who managed to escape.
"I accept that (Flett) did not mean to harm anyone, but simply wanted to scare them," McCawley said.
"However, she was not incapable of appreciating that something bad could happen as a result of setting the fire."
The judge took into account a psychological report that said Flett had below-normal intelligence and a harsh upbringing on a remote aboriginal reserve. She had suffered physical and sexual abuse as a child, court was told.
McCawley, saying the crime was simply too serious, rejected a defence request for a sentence of eight to 10 years.
"The court must ... affirm society's respect for human life and dignity."
McCawley's sentence for Flett was actually life in prison with no chance of parole for seven years, but the judge gave Flett two years of credit for time already served.
Flett is also banned for life from possessing weapons.