A 45-year-old Hamilton woman is beginning a 22-month prison term today for having sex with a 15-year-old boy.

The woman, who has permanent name suppression to protect the identity of her victim, seduced the boy when he had run away from home and was looking for somewhere to spend the night.

The boy went to her home on December 27 as he knew the woman's daughter, but when he go there the 45-year-old was the only one home.

In Hamilton District Court yesterday, Judge Philip Connell said the woman had been drinking that evening and while the boy was at the computer had leaned over and kissed him.

"He didn't want anything to happen but felt powerless to stop you," Judge Connell said.

Despite the boy's protestations, the woman removed his shirt, jeans and underwear, then had sex with him, the court heard.

He got dressed and left straight after the attack.

The heavy-set woman was charged with sexual connection with a young person, a charge carrying a maximum penalty of 10 years in prison.

The incident is only one of a handful that has gone through the courts since law changes that treat men and women equally as sex offenders were passed more than six years ago.

Judge Connell said she was lucky the charge laid was not more serious.

"You knew at the time he was too young to be making any proper judgment, and that to me is very close to acknowledging that he wasn't, in effect, consenting," he said.

The woman was sentenced to 22 months' prison, which was converted to 11 months' home detention, to be served with her father at his retirement village, but at the eleventh hour the judge noticed she would only have been permitted to stay there for three months, making the address unviable.

She had pleaded guilty to the charges at an earlier hearing.

Instead, the original jail sentence stood, much to the woman's shock, as she was ushered into custody.

Though she was given name suppression, Judge Connell said it was a close-run thing and "the public should be aware she could well be a predator in terms of this sexual offending".

Defence counsel Melissa James pointed to her client's clean criminal history, and her "absolute disgust" at her own behaviour on the night.

It was a one-off incident and there was no grooming involved, but Judge Connell highlighted the "powerful" victim impact statements from the 15-year-old and his mum, which told of the emotional hardship caused by the incident and ongoing trauma he faced.

Hamilton-based clinical psychologist Luanda Young, speaking to the Waikato Times after yesterday's sentencing, said though she had never worked with a young male victim who had been abused by an older female, she would not be surprised if it was just the tip of the iceberg.

"With females it's more common so the disclosure is easier ... With young males it's not, so it's more difficult," she said.

Despite it being a one-off, she said it would have a definite impact on the boy.

At his young age it could skew his sexual and emotional development, as well as his personal identity.

The court heard the offender had also been abused when she was younger.

She was also convicted yesterday of assault against her 14-year-old daughter, who was not living with her now.

It stemmed from an incident in June when she grabbed the girl by the throat before throwing her to the floor.

The woman is understood to have kneed the girl in the ribs in the attack.

CHILDREN EXPLOITED

May 2009: A 36-year-old mother of two was sentenced to a year of home detention, and 200 hours of community work for having sex with her best friend's 15-year-old son.

April 2007: A woman who had sex with two underage boys in a cowshed was found guilty on six counts of sexual violation and jailed for three years.

December 2005: Solo mother Briar Jayne Dravitski, 23, pleaded guilty in New Plymouth District Court to two charges of performing an indecent act with a boy who was 13 but led her to believe he was 17. She was sentenced to 240 hours of community work and nine months supervision.

April 2003: Swimming instructor Stacey Margaret Friel, 21, was reported to have had sex with a 13-year-old boy. She met him while working as a swimming instructor but did not coach him, so could not be prosecuted as the law had not changed.