Alberta's Court of Appeal has ordered a new trial for an Edmonton foster mother who was found guilty of manslaughter in the death of a three-year-old boy in her care.

The woman cannot be named under Alberta's child welfare legislation. She was originally charged with second-degree murder, but a jury found her guilty of the lesser charge of manslaughter at her trial in November 2008. She was sentenced to three years in prison.

Both the Crown and the woman's lawyer appealed the outcome of the trial to the Alberta Court of Appeal. The defence asked for an acquittal on the manslaughter conviction. The Crown appealed her acquittal on the murder charge.

In a ruling released Friday, the appeal court judges ordered a new trial on the original second-degree murder charge after finding that the trial judge made a "legally incorrect exhortation" to the jury to reach a verdict after they said they were deadlocked.

The exhortation had elements in it that contravened policy set out in a 1996 court ruling, the appeal court judges found.

"Those elements involved references to the need to re-try the case with its associated inconvenience, expense and hardship for the Crown and the defence, and the association of that negative result with 'the unwillingness of one or more of their number to listen to the arguments of the rest,'" the ruling says.

The little boy died in January 2007 of a massive head injury, the court heard during the trial. The child also cannot be named under Alberta legislation.