His latest offending took place in a house in Northland in 2011.
The victim's mother and her stepfather read out victim impact statements in court.
After the attack on her, the teenager said she only trusted her parents, brothers, an aunt and her teacher.
She felt no one believed her but thought otherwise after Hetherington was found guilty on the charges.
Her mother said 28 months after the offending, the girl was still undergoing counselling.
"How dare he attack her in bed where she was supposed to be safe?" the mother asked.
Her parents didn't talk to her about the attack until after Hetherington was found guilty to avoid the risk of affecting the evidence during trial, Justice Pamela Andrews said.
Hetherington refused to be interviewed by a psychologist and a psychiatrist as he continued to maintain his innocence, the judge said.
She said Hetherington was likely to commit further offences as treatment had little or no effect on him outside prison.
Prosecutor Anna Patterson said Hetherington was a predatory offender with a history of preying on pre-pubescent girls.
The victim, she said, was highly vulnerable due to the huge age gap between her and Hetherington and her mental state, coupled with a speech impairment.
Ms Patterson said there were features of grooming the victim such as Hetherington making comments to her such as: "You're sexy. I'd like to have babies with you" prior to his offending.
Defence lawyer Mike Dodds submitted that a finite sentence rather than preventive detention should be imposed. The real risk, he said, was Hetherington's drinking and his sexual arousal towards adult females.
