Warning: Some readers may find the details in this story disturbing

A 49-year-old Kitchener, Ont. woman has pleaded guilty to taking part in the sexual assault of a seven-year-old Hamilton girl who was allegedly advertised on Craigslist by her mother's boyfriend.

Sonya Lucas pleaded guilty Tuesday to sexual interference, making child pornography, and possession of child pornography.

In an agreed statement of facts, Lucas admitted she travelled to Hamilton with a Waterloo man named Rui DaSilva, who had responded to the Craiglist ad about the girl. He had then hired Lucas, who worked in the sex industry, to be his escort.

Lucas and DaSilva travelled to the girl's home in the middle of the night and sexually assaulted the girl. Court heard that Lucas did not expect a girl to be involved in her encounter with DaSilva, but did nothing to stop it when she realized DaSilva’s plan.

“No one held a gun to her head and forced her to stay there,” Lucas’ defence lawyer Hal Mattson told CTV Kitchener. “She doesn’t have the defence of ‘duress.’ That’s why she pleaded guilty.”

Lucas admitted to inappropriately touching the girl, while at the same time taking cellphone video of two men sexually abusing the girl.

During the hearing Tuesday, the video was played to the judge who had difficulty viewing it and looked away from the screen from time to time.

DaSilva pleaded guilty last month to various criminal offences in connection with the same investigation. He is awaiting sentencing.

The case involving the mother’s boyfriend, who cannot be named because it could identify the victim, is still before the courts.

This isn’t the first time Lucas has faced serious accusations of abusing minors; she has a prior conviction for sexually assaulting children and is registered as a sex offender.

During Lucas’ court appearance Tuesday, she teared up when she saw her son sitting in the front row. The son, who doesn't want to be identified, spoke to CTV Kitchener and said he has a hard time forgiving his mother for what she did.

“I would have to say that someone who does those things to children is a monster,” he said.

The Crown will be seeking a prison sentence of eight to 10 years for Lucas. Her son said he hopes the sentence is a strong one.

“Hopefully, the judge is going to hand down a sentence that is going to make an example of her and anyone else who decides they want to prey on kids and hurt them,” he said.

Lucas faces sentencing in September. Her lawyer, Mattson, said there will be “no winners in a case like this.”

The arrests in the case stemmed from a Hamilton Police investigation called Project Links. That investigation began in May, 2016, with a tip from the Hamilton Catholic Children’s Aid Society who reported that a young girl claimed she was being molested by her mother’s boyfriend.

With a report from CTV Kitchener’s Nicole Lampa