The 55-year-old woman this week pleaded guilty to sexual penetration of a child and committing an indecent act with a child.
Her 42-year-old nephew pleaded guilty to persistent sexual abuse of a child under the age of 16.
The pair, who were in a sexual relationship when the offending started in 2011, appeared briefly in the Victorian County Court on Friday, where sentencing was set down for June 24.
The court had previously heard the mother and nephew began their relationship shortly after he let the woman and her daughter live in one of his houses after she had split from her husband.
On one occasion while the pair were having sex, the nephew started touching the daughter.
The daughter was raped for the first time shortly after, while her mother held one of her legs so she could see what was happening.
The rapes continued until 2014, when the girl was 15, although the mother was not involved again.
It was usually when the girl was alone in the house with the nephew.
The man was arrested in December 2014 after the teenage victim told her older siblings about the attacks.
