The Quebec Court of Appeal set aside the guilty verdict of a woman convicted in 2013 of murdering her two daughters and has ordered a new trial.

Adele Sorella was convicted of first-degree murder in the 2009 deaths of nine-year-old Amanda and eight-year-old Sabrina in the family home in Laval, Que., north of Montreal.

The trial judge in her case gave erroneous directives to the jury, the appeals court ruled Monday.

Moreover, the court ruled a video shown during the trial of her police interrogation was prejudicial.

Trial judge gave problematic directives around the issue of "reasonable doubt," wrote Justice Martin Vauclair, on behalf of the appellate court.

He said Cohen erred by giving jurors directives regarding the Criminal Code section of criminal non-responsibility by way of mental disorder, which was not Sorella's defence.

"(Cohen's) directives could not help but cause confusion," Vauclair wrote. "That constitutes (a) motive to order a new trial."

There were no marks of violence on Sorella's two girls, but the Crown argued the children had died by asphyxiation by cutting off the oxygen supply in a hyperbaric chamber.

The chamber had been used to treat Sabrina's juvenile arthritis.

Sorella is the ex-wife of Giuseppe De Vito, a convicted Quebec mobster who was found dead in prison in 2013 and, according to a coroner, was likely poisoned with cyanide.

The children died while De Vito was on the lam for conspiracy and cocaine trafficking charges.

- With files from CTV Montreal