A Victorian woman lied to police about sexually abusing a boy because she did not want the offending to "ruin her life".

The 39-year-old on Friday pleaded guilty to two counts of sexual penetration of a child under the age of 16.

The mother initially denied the abuse when interviewed by police in 2015 before telling them "something that lasted five seconds can ruin my life forever", the prosecution told the County Court of Victoria.

The boy went to school with the woman's daughter and was 14 at the time.

The then-36-year-old woman performed sex acts with the boy on two separate occasions at her home.

"It's so wrong on so many levels," the woman later told police.

"I've done some stupid things."

The woman told detectives the sex acts were consensual.

"It's not just me - he has been part of this as well," she said.

The mother told police the 14-year-old had instigated the sexual contact and that she had tried to "push him off".

"I never gave him any indication that I wanted to be with him or touch him."

But according to the prosecution the woman asked the boy if she could touch him.

She subsequently acknowledged the gravity of her crimes and said she felt horrible about what had happened.

She hoped the complainant would be able to live a normal life, the court heard.

After he was abused, the teenager became depressed, underperformed at school, and tried to numb his feelings with alcohol.

His parents did not understand the changes in their son until the offending was exposed.

He was diagnosed with post-traumatic stress disorder and despite having treatment, was still struggling with what happened, his mother said.

"To watch your child suffer is heartbreaking," she told the court in a victim impact statement.

"My heart is breaking for the son that I have lost and I can only hope to find him again."

The pedophile will be sentenced at a later date.