A teenager who admitted murdering a mother-of-three by setting her house alight was today jailed for a minimum of 11 and a half years.

Name suppression for Tonia Ashleigh Bennett, 18, was today lifted when she appeared in the High Court at Auckland for sentencing. Name suppression continues for the man who accompanied her the night of the murder.

Bennett in March pleaded guilty to murder and two counts of arson relating to the death of Pukekohe mother Lynette Chapman. Her guilty plea came before her trial was due to begin in April.

She told police she knew Ms Chapman was at home, probably sleeping with the television on, when she started a fire that blocked the woman's chance to escape and left her to die.

In the dock today Bennett sat fidgeting and crying and avoided eye contact with Ms Chapman's three sons. As the victim impact statements were read out she appeared to be fighting tears.

Ms Chapman's son Brad spoke directly to her when reading his statement, asking her why she did it and saying his life would never be the same.

Justice Geoffrey Venning gave Bennett credit for her early guilty plea but said her offending had a massive impact on Ms Chapman's family.

"Your offending on the night was stupid and had a tragic result but was committed in the context of your very troubled personal circumstances," he told Bennett.

Bennett's lawyer, Clare Bennett, said the jail time would be the most stable her client would have ever had.

On January 20, 2009, Bennett and a 19 year-old man went to Ms Chapman's house and set alight a T-shirt on the front step. The man in March pleaded guilty to manslaughter and arson and was jailed for two years.

Disappointed the T-shirt burned out quickly, Bennett - then aged 16 - took a sweatshirt, belonging to one of Ms Chapman's sons, and entered the house where she set it on fire by the stairwell. She also poured absinthe on the floor.

She later admitted to police she heard the television playing upstairs when she approached the house, knew Ms Chapman was home, and had earlier spoke of knowing, "Lynette sleeps with her television on all the time".

Normally Ms Chapman's sons Brad, Todd and Cole would have been home, but they were staying at their father's house elsewhere in Pukekohe.

After Bennett started the fire she went back to her house with the 19-year-old, where her caregiver heard them speak about what happened.

Neighbours heard the fire but couldn't help because the house had been engulfed in flames.

Firefighters found the stairs had been completely consumed by fire so had to get to the upper storey using ladders through an upper window.

The fire was so fierce the front door had been sucked inwards and off its supports.

Ms Chapman was found in her bedroom with her head at the foot of the bed. A pathologist report to police said she had been overcome by smoke.