Ms Whittaker said they were exchanging sexually explicit text messages, initiated by Godfrey.
Three days before they had sex, she told him her age - an "age disparity of 11 years".
Godfrey is already serving a three and a half years in prison for stabbing a man in the buttocks.
Ms Whittaker said the totality of the sentence could be looked at to reflect the gravity of the offending.
Defence lawyer Jock Blathwayt said his client was remorseful and was lonely, suffering from depression.
"His judgment was obviously affected by that. His very early guilty plea indicated the degree of remorse."
Mr Blathwayt said he took issue with the Crown's submission that Godfrey was grooming the girl.
"It's clear his knowledge didn't arise until two days before sexual intercourse taking place.
"There's no excuse of course, an adult should have known.
"It was not close to sexual violation, whatever happened here was entirely consensual."
Judge Morris said the maximum prison term for the charge was 10 years.
She said Godfrey originally denied having sex with the girl and denied knowing her age.
The victim impact statement revealed the impact of the offending, she said.
It damaged the relationship between the daughter and her mother "in a time in a teenager's life when they have much need for that support".
Judge Morris said the probation report found he was at a moderate risk of harming others.
"It acknowledges you had real remorse, you felt guilty about what you had done."
The report also said Godfrey suffered significant depression.
"None of that is to make an excuse as to what happened but it is a background," she said.
"The offence is very serious ... it was certainly not a momentary lapse of judgement."
Judge Morris said what he did couldn't be described as grooming. "That age gap makes it all the more serious, as does the extent of harm."
She said looking at these factors, two years three months was a start point but reduced it based on his plea and the sentence he was already serving.
"It is also important [the guilty plea] because the victim does not have to give evidence in a gruelling trial." She sentenced him to one year and two months.
The victim's mother was at court for the sentencing but declined to comment on the outcome.
