A teenage girl who plotted to kill her entire family by stabbing them to death has been sentenced to ten to 20 years in prison.

Roksana Sikorski was 15 when she attempted to carry out a plan she had hatched with her 23-year-old boyfriend, Michael Rivera.

The teenager crept into her 12-year-old brother's bedroom at their home in Detroit, Michigan, in October 2014 and slashed his neck with an 8-inch fillet knife.

Throughout the attack, Roksana, now 17, was communicating with Rivera using emoticon-littered texts, including one debating the best weapon to slit an artery in the throat, NBC News reported.

"I feel like dad is waking. He's moving but snoring. Babe..?" Roksana wrote in one message to Rivera, according to WDIV-TV, to which he responded, "Baby im here just cut the throat quickly on both of them."

In another she wrote: "Babe I can't f----ing do it. I'm too scared. I want u to do it.... :( Plzz baby plzz. He kept waking up."

After stabbing her brother, she moved on to her 11-year-old sister, but both children managed to survive and their screaming scared their sister off.

Roksana was tried as an adult on charges that included assault with intent to murder and conspiracy to commit murder.

She apologised to her parents in court on Monday.

"She still can't believe that she did it," her lawyer, Leslie Posner, told NBC News. "She's vivacious and outgoing. She gets As in every class. She's tutoring other students. It was just a bad event."

Posner said the "sweet, little, diminutive 15-year-old" was "petrified" of Rivera, who she met on Facebook.

Roksana and her two siblings were adopted by Laurene and Jeff Sikorski from an abusive family in Poland more than ten years ago.

Before the attack, her parents had filed a statutory rape complaint against Rivera. The defence argued that is when Rivera convinced her into the murders.

"I think she just thought this guy loved her and she wanted to do whatever he told her, and she was very vulnerable and she has a mental disorder and she needs help," Laurene Sikorski told WDIV-TV.

Roksana’s parents have stood by their daughter and requested that she not be tried as an adult.

Judge James Callahan told the family he would try to request Roksana to be housed in a juvenile facility until she turns 18.

Rivera is now serving a lifetime prison sentence for attempted murder and conspiracy.