NASHUA, N.H. (AP) – An 18-year-old woman was sentenced Thursday to 40 years to life for plotting with her boyfriend to murder her mother in 2003.

Nicole Kasinskas didn’t speak at her sentencing in Hillsborough County Superior Court, but Jeanne Dominico’s family and friends told the court about how the murder had affected them.

Kasinskas agreed to plead guilty to second-degree murder. In exchange, she testified against her former boyfriend, 20-year-old William Sullivan of Willimantic, Conn. Sullivan was convicted in July of first-degree murder.

With credit for time served and education incentives, Kasinskas will be 51 before she’s up for parole.

Prosecutors say Sullivan, then 18, and Kasinskas, then 16, plotted to kill her 43-year-old mother because they wanted to live together and she opposed it.

Sullivan’s lawyers say he was insane when Dominico was killed.

During her testimony, Kasinskas has described how her intense, obsessive relationship with Sullivan blossomed soon after they struck up correspondence over the Internet.

She described how she and Sullivan tried several times to kill her mother over the days leading up to the bloody end.

Sullivan’s lawyers have argued the murder itself proves he was crazy, but Kasinskas described a deliberate, concerted campaign to kill Dominico, spanning days.

Kasinskas described Sullivan as the driving force, coming up with plans to poison her mother’s coffee, set fire to her bedroom, blow up the house by igniting the oil tank and then, finally, beat her to death, and make it look as though someone had broken into the house.

In a videotaped police interview played at his trial, Sullivan said the idea of killing Dominico was a joke a first, then a fantasy he never thought he would carry out. The day he did it, he said he and Dominico were arguing in her home when she turned her back.

He said he hit her in the back and head with a baseball bat, then stabbed her repeatedly. Once he began to stab her, Sullivan said, there was no stopping.