Peta Butler was 15 years old when she was taken to a Toowoomba hotel where her mother arranged for a man to rape her.

Detective Senior Constable Jodi Bell said it took Ms Butler until 2016 — more than a decade later — to work up the courage to approach police, who are still trying to find the man responsible.

"Her mum had taken her on a bus ride, on the guise of having a girls' night away for her birthday. And they then went to a hotel room where there was a man waiting," Senior Constable Bell said.

"It takes a lot to walk into a police station and speak to a complete stranger about being violated. Especially when it's a family member."

In January, her mother Therese Butler was sent to jail over the assault, using a long phone call recorded by Peta as evidence.

"In that phone call she was able to get her mum to admit that she had arranged for this male person to rape her daughter," Senior Constable Bell said.

Peta Butler said she thought she was having a girls' night out with her mother. ( Channel Nine: ACA )

In the taped call, Therese Butler claimed her daughter was 16 at the time, above the age of consent, and used that to help justify her actions.

Peta Butler: I told him no, I was crying, I was telling him no. Therese Butler: It was still, yeah, it was still rape, but you were 16. I wouldn't let him touch you under, under 16, no way.

Police have completed a computer-generated image of the rapist, known as Thommo, who assaulted Ms Butler some time between May and December 2005.

He is described as being in his mid-to-late 40s at the time, extremely obese, 175 centimetres tall with a shaved head, stubble and distinctive bulging blue eyes, with dark circles underneath.

A computer-generated image of a man police believe raped the then 15-year-old. ( Supplied: QPS )

He was wearing an expensive suit and drove a car with cream-coloured leather seats.

Police hope members of the public will come forward to help identify the man, who would now be in his 50s.

He may also have used an email address similar to thommo_thommo_thommo@hotmail.com.

"Any information that the public may have even if you think it's minor to you, please call Crime Stoppers," Senior Constable Bell said.

She said it was likely the man had hurt other girls and women.

Mother sat next door smoking during rape

The case has received considerable media attention in recent weeks.

Last night, Ms Butler told Channel Nine that before going to the hotel in 2005, her mother took her to a bottle shop and encouraged her to drink pre-mixed vodka drinks.

Therese Butler is serving a jail sentence for her role in her daughter's sexual assault. ( Facebook: Therese Butler )

"When we were walking she said 'oh drink this because it will make you warmer,'" she said.

She said her mother sat in the room next door smoking during the rape.

"I was hoping she was going to come in and stop it. She didn't once try, " she said.

"She set it up and she took me to the place … she premeditated the whole thing. That's not a mother."

Ms Butler said she was still angry at her mother for her "betrayal".

"Probably within a week of it happening I dropped out of school. I lost a lot of friends along the way because of how I rebelled. I went into depression, I was anxious all the time."

Senior Constable Bell said police wanted to reassure victims of rape and sexual assault that they would be believed if they spoke to authorities.

"Don't be scared, we will help you," she said.

She praised Ms Butler for her bravery in telling her story.

'It happens more often than people realise'

Child protection advocate Hetty Johnston from Bravehearts said the incident was "absolutely appalling", but not uncommon.

"Children being used for sex and sold for sex does happen, and it happens in much greater numbers than what we really talk about," she said.

She said Therese Butler's actions were unthinkable, and praised Peta for coming forward.

"It is important to report abuse and it is incredibly important that victims themselves ... come out and encourage other survivors and victims of sexual assault to come forward," Ms Johnston said.

She said she hoped Peta had gained some closure and could move forward.

"I hope that she has been relieved of the ball and chain of shame and secrecy and silence of coming forward and getting this result."