Carlota Prado was told about the alleged attack, which happened after an alcohol-fuelled party, when she was a contestant on the 2017 series.
She had started a relationship with fellow contestant Jose Maria Lopez and was called into the diary room to watch Mr Lopez allegedly sexually assaulting her while she was unconscious.
“Please, Super, stop now, please.” she said in tears, as she was shown the footage.
“We think you need to see this, Carlota,” the voice of the diary room replied.
The alleged incident, which is said to have happened under the bed covers, was never aired on the show Gran Hermano Revolution, which is broadcast on Spanish TV channel Telecinco.
El Confidencial recently obtained footage of the diary room scene from two years ago.
Ms Prado, a former nightclub promoter who was 24 at the time, told the digital newspaper: “There should have been someone at my side, a psychologist or someone who would help me face those really difficult images.
“They never asked me if I wanted to see that (the images)… if they asked, I would have said no.”
Mr Lopez was expelled from the show at the time, while Ms Prado took a break for a few days before returning to the show.
Zeppelin, the production company that makes the show, reported Mr Lopez to the police and Ms Prado later also made a complaint.
A judge investigating the case recently recommended putting Mr Lopez on trial.
Mr Lopez’s lawyer, Antonio Madrid, told El Confidencial the former contestant denies the allegation of sexual assault.
Several companies have pulled their advertising from the TV show following the revelations.
Ricardo Cirujano, spokesman for Carretilla, which produces microwavable meals and tinned asparagus in Spain, told AFP news agency the firm had withdrawn its sponsorship of the programme “like so many other brands” because “it does not share its values”.
In response to a direct tweet from a member of the public about its advertising, Nestle Espana wrote: “Hello, we totally reject any type of gender abuse or violence and we have decided to withdraw advertising in these circumstances.”
In a statement, Endemol Shine Group, which owns the company that produces the show, said “no footage was ever shot with the intention of being broadcast”.
It said that “in hindsight we regret that the conversation in which Carlota was informed took place in the diary room”.
“The footage was only supplied as evidence when requested by the authorities, encrypted and guarded,” it added in a statement.
Telecinco’s owner, Mediaset Espana, said in a statement that it was the victim of a campaign to “discredit” it on the part of rival media groups.
The company added that it “would remain attentive to the results of the investigation and the total clarification of the facts, respecting the privacy of the people affected”.