This was the daughter who used to run from her Wollongong home to the bush creek to scrape her skin clean in the cold water.

"I stayed there for hours and hours, hoping they didn't come to find me," she told the Sydney Downing District Court on Friday. "My skin felt like a brick."

Her mother, who sexually abused three of her then five children in the 1970s, is known for legal reasons as DW.

But to the daughter who gave evidence against her, she is "the old hag".

"The abuse ruined my life because I lost my dignity before I met my husband," she said in a victim impact statement.

Now, she said, she did not go to parties or even the supermarket. "You just lock yourself away to the day you die."

DW denied all nine allegations of abuse against her twin daughters, as well as others against her son, but she was found guilty in two separate cases.

In his sentencing remarks, Judge Peter Berman said DW first assaulted her daughter when she was five years old.

She took her daughter into her bedroom, told her to undress and then get into bed. DW also undressed and climbed into bed, where she forced her daughter to perform different sex acts on her.

When the same girl was eight or nine, she and her twin sister were forced into a similar situation. In their mother's bed, they were sexually assaulted until their older sister interrupted the scene, telling the young girls to dress and leave the room.

The court heard DW had had a happy childhood and no criminal record. She was, however, "significantly intellectually disabled". Her husband at the time of her offending had also abused the children.

"Anyone attempting to find a clue as to why DW would abuse her children in the way she has would immediately suspect that it was her relationship with her second husband which caused these offences," Judge Berman said.

The judge said he was bound by law to sentence DW as if it were still the 1970s, which meant being more lenient than he wished.

"In the 1970s, the courts had an approach to sentencing offenders such as DW that we now know to be wrong," he said.

For the offences against her daughters, DW was sentenced to nine years' jail, with a non-parole period of 4 ½ years. Together with the jail term for the abuse of her son, she is serving a minimum 12 ½ years in prison.

She would be eligible for parole at age 83.

Meanwhile, her daughter still has a place in the bush where she retreats, a place no one knows about. "I have a tent there," she told the court. "That's my safe place."