Elaine Campione drowned her daughters, Serena, 3, and Sophia, 19 months, in the bathtub in October 2006 while in the midst of a custody battle with her ex-husband.
Court heard the Barrie, Ont., woman had been diagnosed as having unspecified psychosis and other mental illnesses, but a jury found that did not prevent her from knowing it was wrong to drown her children, as the defence had suggested.
She was convicted of first-degree murder and sentenced to life in prison with no parole eligibility for 25 years.
In appealing her convictions, Campione said the trial judge made three errors in instructing the jury on how to determine whether she should be found not criminally responsible.
But the appeal court found the trial judge properly instructed the jury on the law.
"The jurors were made well aware that, if they accepted the appellant’s version of the killings, they had to render a verdict of NCR. I see no basis for confusion on this issue," the three-person panel wrote in its decision.
"While the focus of the test is on the appellant’s state of mind and her capacity for rational choice, the question is not whether the appellant considered the acts justified according to her own moral code, but whether she was incapable of knowing that her actions were contrary to society’s morality."