A Toronto judge has decided that the teenage girl convicted in the murder of 14-year-old Stefanie Rengel must take responsibility for the crime as an adult.

Melissa Todorovic, 17, was sentenced as an adult for first-degree murder. She will serve a sentence of 25 years and will not be up for parole until after she has served at least seven years of her sentence.

The girl, who up until this morning was known only as M.T. because she was convicted as a young offender, is said to have orchestrated the stabbing that killed Stefanie on New Year's Day 2008.

The publication ban on her identity was lifted when the judge sentenced her as an adult.

When Justice Ian Nordheimer announced the sentence, there was a collective gasp in the courtoom, according to a reporter who was inside during the proceedings. Several people started crying and one person started to clap, the reporter said.

Todorovic and her family were "devastated" by the sentence, said the girl's lawyer Marshall Sack.

"They cried, you saw them cry. They're devastated," he told reporters gathered outside the courtroom.

He said he is advising the family to appeal the findings of the court and the sentence, saying the violence was "unprecedented in her life" and that she is not likely to reoffend.

Stefanie's 13-year-old brother Ian read out a brief statement to reporters on behalf of his family.

"No judgment can ever bring back Stefanie," he said. "No ruling can bring her back."

"Melissa Todorovic is a disturbed individual who needs all the help that our system has to offer," he added.

He said his family is praying that the girl will be rehabilitated in prison and will grow up to be a balanced adult.

'Puppetmaster blameworthy'

Stefanie's murder trial made headlines for the shocking evidence that was brought forward by the Crown, depicting Todorovic as a manipulative temptress.

A forensic psychiatrist who testified at the sentencing hearing likened the teen to Glenn Close's character in the 1987 thriller "Fatal Attraction."

The Crown told a jury during the trial that Todorovic was jealous of Stefanie -- a girl she had never actually met. Stefanie briefly dated the teen's boyfriend.

Court heard that Todorovic threatened to withhold sex from her boyfriend and break up with him if he didn't kill Stefanie.

The boyfriend, known to the courts as D.B., plead guilty to first-degree murder, after luring Stefanie out of her East York home and stabbing her six times. He then left her to die on a snow-covered sidewalk steps away from her home.

Toronto police homicide Squad Det. Sgt. Steve Ryan said the one thing that stood out about Todorovic during their investigation was her "lack of remorse."

"Death is permanent and there's no second chances," he told reporters when he was asked about the message that was being sent to young people. "There's a price to pay. It's not a video game where you press restart and it's over."

He said he feels relieved for the family and wished them some closure.

Nordheimer addressed Stefanie's family after he handed down the sentence, telling them that he sympathizes with the "loss, sorrow anger that you feel."

"You must realize whatever decision I make will not change the reality (of Stefanie's murder) or lessen your sadness," he said. "There's nothing the justice system could do that could ever right such a wrong."

The judge went on to say that Todorovic has a "frightening" character flaw.

"The puppetmaster is not less blameworthy than the puppet."