A Melbourne mum who assisted in her daughter's rape may be free within a year.

Trigger warning: This post deals with child sexual abuse.

A mother who helped her adult nephew rape her pre-teen daughter has been jailed — but she may be free in as little as a year.

The Victorian County Court sentenced the woman on Friday to a maximum of four years’ jail with a minimum of two years for the horrifying attack, Fairfax Media reports.

But the Melbourne woman has already served 453 days in jail for breaching her bail conditions, and that time already served will be deducted from the two-year minimum sentence.

The court was told that the mother, who cannot be named to protect the girl's identity, moved into a Caroline Springs home owned by her adult nephew in 2011, after her marriage broke down.

The woman, then 50, and her nephew, who was then 35, fell into a sexual relationship.

On one occasion, the court heard, while the pair were having sex, the nephew started touching the daughter.

It was just after this that the young girl was raped for the first time -- and the mother assisted in the abuse by holding the girls' leg in place, as Mamamia previously reported.

"The girl is crying and it's hurting . . . and [the mother] holds the leg so she can see what's happening," prosecutor Michael Hennessy said, referring to one sickening attack.

He  referred to the abuse as: "The breaking of the virginity."

While the woman was not involved in any further abuse, the man sexually abused the girl until she was 15, Fairfax Media reports.

The assaults took place when the girl's mother was not present.

The nephew and the girl’s mother were finally arrested in December 2014, after the daughter told her older siblings about the attacks.

The Melbourne man pleaded guilty in the County Court of Victoria to persistent sexual abuse of a child under the age of 16. The girl’s mother, now 55, pleaded guilty to sexual penetration of a child and an indecent act with a child.

The man was bailed, but the mother has been on remand since March after she broke her bail conditions by contacting her daughter a number of times.

The nephew's defence lawyer, Ashley Halphen, said the nephew had expressed remorse in a letter to the daughter, who is now 17.

But the judge wasn't convinced.

"Reading the whole tenor of it, I don't see it," Judge Claire Quin said.

Lifeline 13 11 14. Kid's Helpline: 1800 55 1800. DV and Sexual Abuse hotline 27/4: 1800 737 732. Survivors of childhood sexual assault can call Bravehearts help line on 1800 272 831 or go to www.bravehearts.org.au.