TORONTO - Melissa Todorovic, who was handed a life sentence for orchestrating the stabbing death of Toronto teen Stefanie Rengel, has filed for an appeal of her first-degree murder conviction and sentence.

Todorovic, who was just shy of her 16th birthday at the time of the 2008 killing, was convicted of first-degree murder and given an adult sentence of life in prison with no chance of parole for seven years.

In appealing the decision, Todorovic claims her sentence was "unreasonable and excessive," the verdict was unreasonable and "based on an error of law" and that Ontario Justice Ian Nordheimer erred in admitting certain evidence and in passing an adult sentence.

Todorovic signed the appeal documents on Aug. 26, about a month after she was sentenced, and the documents were filed Oct. 15 at the Ontario Court of Appeal.

The day Todorovic was sentenced, her trial lawyer Marshall Sack said his client would appeal her conviction.

Rengel was lured from her home on New Year's Day 2008 by Todorovic's then 17-year-old boyfriend, David Bagshaw, who pleaded guilty to stabbing the 14-year-old girl six times and leaving her to die in a snowbank.

Bagshaw was also handed a life sentence with no chance of parole for 10 years.

Nordheimer had described Todorovic as the "puppet master" in the murder and gave her the maximum sentence for first-degree murder committed by someone under 16 at the time of the offence.

The court heard how she mistakenly viewed Rengel, who had been in a brief and non-sexual relationship with Bagshaw when she was 12, as her romantic rival.

Todorovic "engaged in an unrelenting campaign over many months to cause the death of a 14-year-old girl that she had never met," Nordheimer said during Todorovic's sentencing on July 28.

She placed "relentless pressure" on Bagshaw through instant messages, text messages and Facebook messages threatening to withhold sex from him if he didn't kill Rengel.

Sack had maintained that Todorovic was less culpable than Bagshaw because he was the one who actually stabbed Rengel, but Nordheimer disagreed.

"Put simply, the puppet master is not less blameworthy than the puppet," he told the court. "Indeed, I would suggest that the master is more culpable."

Nordheimer also sentenced Bagshaw, now 19, calling Rengel's stabbing a "truly evil" act.

The court heard how Bagshaw went to Rengel's home the night of the murder and lured her outside, then stabbed her with an eight-inch kitchen knife and left her to die.

He disposed of the knife and his bloodstained jacket at a friend's house, phoned Todorovic to "report the success of his mission," then went to her house to collect his "reward" -- sex, Nordheimer said.

"I accept that David was the more reluctant of the two partners in this evil endeavour, but that does not change the fact that he knowingly and actively participated in it," the judge said during Bagshaw's sentencing on Sept. 28.

"Melissa may have given the orders but it was David who carried them out."