The Court of Appeal of Alberta has upheld the manslaughter conviction of an Edmonton foster mother found guilty in the death of a three-year-old boy in her care.

Lily Choy was convicted of manslaughter during her second trial in 2011 and is serving a six-year sentence in British Columbia's women’s prison.

Choy first went on trial in 2008. She was sentenced to three years after a jury found her guilty of the same charge but she was granted a new trial after the conviction was overturned on appeal.

Her lawyer argued last week before the Court of Appeal that the judge in the 2011 trial erred in assessing Choy's credibility on the witness stand and how she evaluated the evidence from witnesses.

He wanted Choy to be granted a third trial. However, the appeal was dismissed in a unanimous decision released on Friday.

The child, who cannot be named under provincial child welfare legislation, died from a fatal brain injury.