EDMONTON - A legal decision from the Supreme Court of Canada is a strange kind of Christmas present, but the mother of the victim in a notorious Edmonton sex slaying will take it.

"We're going to have a good Christmas," Peacha Atkinson said Friday after the top court boosted the conviction against Stephanie Rosa Bird in the death of her daughter Nina Courtepatte.

Bird now stands guilty of first-degree murder rather than manslaughter.

"I've been kind of low for Christmas, but I got good news today so that kind of brings me up a bit."

Bird was one of five young self-described "mall rats" who lured Nina from the fast food outlets and video games of West Edmonton Mall with the promise of a bush party in the early hours of April 3, 2005. Instead, Nina -- just 13 at the time -- was taken to a muddy fairway on a golf course west of the city, raped twice and beaten to death with a sledgehammer.

The crime, seemingly motivated by thrill-seeking and boredom, horrified people and drew national headlines.

During the trials faced by the night's participants, court heard details of a crime plotted two days in advance amidst an aimless teen subculture of hanging out, dining-and-dashing and mall-crawling.

Nina's five assailants chose her from among the youths regularly seen at one of the mall's food courts and convinced her and a friend to leave with them.

In court, all of the accused tried to lay blame on each other. But testimony suggested that Bird, who was 17 at the time, delivered the first blow when she struck Nina on the head with a wrench. Bird also held Nina down while the first man raped her.

Bird left the scene before the fatal beating began, taking Nina's friend back to the car they had arrived in. Bird's lawyer, Colleen Connolly, argued that leaving the scene proved her client didn't want to be part of the killing and that absolved her of first-degree murder.

In a unanimous judgment, however, the Supreme Court concluded there wasn't enough evidence that Bird had had a change of heart.

"As the facts found by the trial judge clearly establish that the murder was planned and deliberate, and involved the unlawful confinement of the victim at the time of the killing, a conviction for first-degree murder is entered," the ruling reads.

Prosecutor Susan Hughson said the court's decision was a vindication of the argument the Crown had used all along.

"We were certainly pleased with the decision," she said. "Given the reasons they provided, they felt it was as strong as we felt it was."

Connolly said her client is concerned that the more serious conviction could curtail the programs she's been part of at the Corrections Canada healing lodge in southern Saskatchewan.

"She's disappointed," Connolly said. "She's concerned about the impact this could have on the treatment and therapy she's been receiving in the setting that she's at, and whether or not she's going to end up being transferred to a maximum institution."

Bird's case will go back to the original trial judge for sentencing. Although she was convicted as a young offender, she was sentenced as an adult on the manslaughter charge.

A second hearing may be held on whether Bird will face an adult sentence for first-degree murder. However, it is considered extremely unlikely that she would now be sentenced as a youth after having been convicted of a more serious crime.

Still, Connolly said she may ask the court to do just that.

"There'll be more conversations before we rule out seeking to have the court revisit that particular issue," she said. "None of us are completely sure what the law is on it."

If sentenced again as an adult, Bird would face a mandatory sentence of life in prison without parole eligibility for 10 years.

Bird's sentencing won't end the legal actions stemming from Nina's murder.

The Crown is appealing the decision of the Alberta Court of Appeal that Joseph Laboucan should get a new trial on his conviction for first-degree murder. Stephen Briscoe, originally acquitted in a 2007 trial, is trying to reverse an Alberta Appeal Court ruling that ordered his retrial.

The Supreme Court has already heard arguments in those appeals.

A third participant, who can't be named because of her age, is involved with three appeals at the provincial level. The Crown is appealing both her conviction and sentence for second-degree murder. The young woman is appealing her conviction.

The fifth participant in the killing pleaded guilty to first-degree murder.

Atkinson, who sat through almost every day of all the original court proceedings, may be spending yet more time in court.

But on Friday, she was content to focus on what she called happy news.

"My kids left (this morning) and they said, 'Now you can have a better Christmas and be happy now,"' said Atkinson. "Nina's going to have a good Christmas and justice is served."