After three days of deliberation, Adele Sorella was convicted by a Laval, Que., jury today in the deaths of nine-year-old Amanda and eight-year-old Sabrina.
Their bodies were found side-by-side in the basement of their Laval residence in March 2009.
There were no marks of violence, but the Crown argued the girls had died by asphyxiation by cutting off the oxygen supply in a hyperbaric chamber.
The hyperbaric chamber had been used to treat Sabrina's juvenile arthritis.
Sorella's ex-husband, Giuseppe De Vito, is currently serving a 15-year sentence for gangsterism and drug trafficking.
De Vito was a surprise witness in the case.
The jury had four choices in the case: first-degree murder, second-degree murder, manslaughter or acquittal.
The first-degree murder verdict carries with it a life sentence with no chance of parole for 25 years.