The country's top court has struck down a manslaughter conviction in a notorious Edmonton sex killing and convicted a young woman of first-degree murder.

In a unanimous decision, the Supreme Court of Canada upgraded the conviction of Stephanie Rosa Bird in the sex slaying of Nina Courtepatte.

Bird is serving 12 years in prison for her role in the death of 13-year-old Nina Courtepatte. The girl was raped and murdered in April 2005, on a golf course west of Edmonton.

"We were bracing ourselves just in case it was bad news," said Peacha Atkinson, the victim's mother. "I'm really hoping it sends a message out to other people who are going through this or who decided to murder people that justice will be served."

Bird was found guilty on the lesser charge of manslaughter back in May of 2008 because she said she had a change of heart and left the scene before the murder. She was 17-years-old at the time of the killing.

The decision by the Supreme Court found that, based on the facts found by the original trial judge, the murder was planned and deliberate and involved the unlawful confinement off the victim at the time of the killing.

Her case will now be returned to the original trial judge for sentencing.

If sentenced as an adult, Bird, who was 17 at the time of the killing, faces a mandatory sentence of life in prison without parole eligibility for 10 years.

With files from The Canadian Press