Prosecutors said lawyers for the the 22-year-old South Australian had secured an agreement which would substantially cut down the time she would serve if found guilty.

Ms Sainsbury was arrested at El Dorado International Airport on April 12, allegedly with 5.8 kilograms of cocaine hidden inside 18 headphone boxes in her suitcase.

A spokesman for the prosecutor told The Australian that "a deal between Fiscalia [the prosecution] and the prisoner which will be made public tomorrow".

Ms Sainsbury is due to return to court for a hearing on Wednesday afternoon, Bogota time.

It is unclear whether the reported deal was struck in conjunction with Ms Sainsbury's Colombian-based lawyer. Her lawyer, Orlando Herran has been contacted for comment.

Ms Sainsbury has previously denied any knowledge of the drugs, and claims she was given the headphones by a man who had been showing her around Bogota.

She said she planned to give the headphones as gifts to friends and members of her wedding party.

Millions tune in for Sainsbury coverage

In May, almost 2.7 million Australians tuned in for competing reports about Ms Sainsbury, aired on Channels Nine and Seven.

60 Minutes and Sunday Night went head-to-head on May 21, drawing in 1.356 million and 1.303 million viewers respectively.

Nine reported that Sainsbury – in the months before her ill-fated trip to Colombia – was a sex worker at Club 220, a brothel 50 kilometres west of Sydney's CBD.

Another Club 220 sex worker said Sainsbury faked her own mother's death for financial gain.

The program expanded on these allegations, with her lawyer claiming the 22-year-old fell victim to an international drug syndicate, threatening to murder her family if she didn't act as a mule.

Her lawyer, Orlando Herron, says the failure of her Australian gym business saw her fall prey to an internet ad, which offered a loan and a free trip to London.

At the last minute, her itinerary was changed to Hong Kong, Los Angeles and then Bogota. This is where a "mystery man" allegedly produced photos of her loved ones, telling her she had no choice but to comply with her demands.

Nine also claimed Sainsbury's fiance Scott Broadbridge was a "person of interest" in Colombia's police investigation.

On Sunday Night, Broadbridge said there were no secrets between him and his fiancee. (Claims about Sainsbury's alleged sex work were not put to him.)

Broadbridge claimed Sainsbury had worked for a cleaning company formerly owned by her uncle. Yet her uncle, Neil Sainsbury, denied he had ever employed his niece – or even owned a cleaning business.

"I believe Cassie has a bit of a history of skipping from one place to the next if things get a bit tough," he said.

"I don't believe she was naive at all, she may have had knowledge, complete knowledge, of what she was doing."

Sainsbury's father said she and Broadbridge had planned – as early as January – to visit Colombia. He claimed they had an argument after he warned her not to do anything "stupid", and she reassured him she wouldn't go.