LAVAL, Que. -- A Quebec mother convicted in the killings of her two young daughters was clearly suffering from mental illness even if she was found criminally responsible for her act, a Quebec Superior Court justice ruled Wednesday as she sentenced Adele Sorella to a minimum of 10 years in prison.

Sorella, 53, was convicted in March of two counts of second-degree murder in the deaths of nine-year-old Amanda and eight-year-old Sabrina. The girls were found dead in the family home in Laval on March 31, 2009.

The jury rejected her defence seeking a verdict of not criminally responsible due to a mental disorder.

In setting parole eligibility at 10 years, Quebec Superior Court Justice Sophie Bourque chose to impose the minimum possible sentence for the crime.

She told the Laval courtroom that Sorella's long history of mental illness was one of the principle factors in sentencing, "even if the defence of non-criminal responsibility was rejected."

Bourque said Sorella's sad history began a decade before her daughters were found lying side by side in their school uniforms on March 31, 2009.

Evidence at the trial revealed that Sorella had attempted suicide three times between 2006 and 2008. In her testimony, Sorella described the psychological distress that followed her surgery for a brain tumour and the disappearance of her husband, Giuseppe De Vito, in 2006 as he was sought by organized crime investigators.

"The psychiatric evidence at the trial is abundant and not contradicted," Bourque said, as Sorella watched from the prisoners box.

Bourque added that Sorella must already live with a verdict that finds her guilty of killing her precious children, and that a longer sentence would be unlikely to have a greater deterrent effect.

While Sorella previously declined an offer to speak in court, she pleaded for her daughters' forgiveness in a letter submitted as part of the sentencing process.

"It is painful and devastating to live without your warm hugs, tender kisses, bursting giggles of laughter each day," she wrote in a letter dated June 7.

"I do not know what happened on that day, and I deeply regret any involvement that I may have had with this terrible and horrible event. I also deeply regret not being there to protect you both, Amanda and Sabrina."

The Crown had recommended that Sorella serve 14 years of the mandatory life sentence before becoming eligible for parole, citing the severity of the crime and Sorella's position of trust over her daughters.

Sorella's lawyers are already appealing her conviction, arguing the verdicts were unreasonable and not supported by the evidence. They did not comment on Wednesday.

A Crown attorney, Nektarios Tzortzinas, said he would take the time to study the judgment before deciding whether to appeal.

The girls' bodies showed no signs of violence, and the cause of death was never established. A pathologist testified that a hyerbaric chamber in the house used to treat Sabrina's juvenile arthritis was a possible cause of death by asphyxia.

Sorella told the court she had little memory of the day when her daughters were found dead, and medical experts testified that Sorella experienced a dissociative episode the day of the killings.

It was the second trial on the charges for Sorella. In 2013, she was found guilty of first-degree murder, but the verdict was overturned in 2017 when the Quebec Court of Appeal ruled the trial judge had erred in her instructions to the jury.