Stefanie Rengel was stabbed six times and left to die in the snow on Jan. 1, 2008. (Toronto Police Service)

A 17-year-old stood in a Toronto courtroom on Friday and said she is sorry and accepts "full responsibility" for her part in the murder of a 14-year-old she suspected was her rival.

The teen, who was convicted earlier this year of first-degree murder in the slaying of Stefanie Rengel, can only be identified as M.T. because of her age.

Rengel was stabbed six times and left to die in a snowbank on New Year's Day 2008 by a male teen who also cannot be named and is only known outside the court by the initials D.B.

D.B. pleaded guilty to first-degree murder earlier this year and is awaiting sentencing.

M.T.'s words on Friday marked the first time she has spoken publicly about the murder.

"I want you to know that I take full responsibility for my part. I know it's hard for you to believe me when I say that," she said.

"I feel very bad for the lives I've ruined and affected. I know you may never forgive me for what I caused and I understand that. But I wanted to share my apology with you. "

M.T. said she wishes she could go back and "change everything" because "no one should have to lose someone they love in a violent, horrific way."

The teenager added that she feels bad for the lives she has ruined, but added she still believes she can still contribute to society in a positive way.

Her lawyer, Marshall Sack, said his client wrote her own statement.

"Her words weren't calculated for effect, they weren't presented for effect. She said them for her benefit and for the benefit of the Rengel family."

The Crown dismissed what it called an eleventh hour apology, reminding the court that two psychiatrists said M.T. continues to see herself as a victim and lacked empathy.

The Crown wants M.T. sentenced as an adult so she will face automatic life imprisonment with no eligibility for parole for five to seven years.

If she is sentenced under the terms of the Youth Criminal Justice Act, she'll face a maximum of six years in custody with a further four years under supervision.

M.T. was 15 when she was driven, according to Crown attorney Robin Flumerfelt, by "vile and obsessive jealousy," to use sexual blackmail via the internet to pressure D.B. into murdering her perceived rival — a girl she had never even met.

During the trial, Flumerfelt cited months of text messages and MSN chat logs in which he alleged M.T. used blackmail to spur her then 17-year-old boyfriend into killing Rengel.

Evidence included online exchanges and the frantic pace of phone calls between M.T. and D.B. that only abated after Rengel's slaying.

M.T. will be sentenced by Justice Ian Nordheimer on July 28.

With files from The Canadian Press