The Pitch Perfect star is being sued by Charlotte MacInnes, the Australian lead actor of the musical comedy The Deb.
MacInnes claims Wilson defamed her in four social media posts which claimed she made a sexual harassment complaint and then retracted it to further her career.
The dispute was sparked when the young actor assisted The Deb's co-producer Amanda Ghost after she suffered a medical episode at Bondi Beach in September 2023.
She helped the producer back to an apartment they were sharing with others and ended up innocently sharing a bath in their swimwear in a bid to warm up, MacInnes says.
Wilson is set to go into the Federal Court witness box on Tuesday after flying from the US with her wife, who will also give evidence this week.
Hints about what she might say can be found in sworn statements by MacInnes that have been tendered to the court and contain parts of the older actor's own affidavit.
Wilson is expected to testify about her claim MacInnes confided in her that Ms Ghost had asked her to have a bath and a shower together, and it made her feel uncomfortable.
MacInnes denies making the complaint, maintaining she later clarified to Wilson the situation had been weird but she was not uncomfortable around Ms Ghost.
In her statement, Wilson says she overheard the producer and young star saying intimate things - often of a sexual nature - to each other, which MacInnes has denounced as untrue.
She also rejected Wilson's account of seeing Ms Ghost push her to go out for a drink together until the young actor relented.
The Bridesmaids star falsely portrayed herself as a whistleblower who spoke up to protect MacInnes when she was actually using the alleged complaint as leverage in a dispute with her co-producers, MacInnes' barrister Sue Chrysanthou SC said.
"I was angry that Rebel claims to be someone who stands up for women … but then was so maliciously and unfairly persisting with a narrative that painted me as a liar, prostitute, sell out, and whore," MacInnes wrote in her affidavit.
Instead of checking on the alleged victim of inappropriate behaviour, Ms Chrysanthou said Wilson instead shared posts "slagging off" her client.
"This is how this bully, apparently this saviour of women, the protector of the harassed, responds," she previously told the court.
But Wilson had raised her concerns with others even though she had doubts about the veracity of the alleged complaint, her lawyer Dauid Sibtain SC said in his opening address.
The central issue is not whether MacInnes was a victim but instead whether she complained to Wilson and then changed her story, he contended.
"Our case is that ... she changed her story," Mr Sibtain said.
"She did so to ensure her career as an actress and musician progressed by appeasing Ms Ghost."
Mr Sibtain argued MacInnes hasn't suffered any harm to her reputation at all as a result of the social media posts, contrary to her allegations.
It is likely Wilson will face questioning about MacInnes' claim she played a role in a hack on her social media account that led to a nude photo being leaked.
The Hollywood star is also expected to be grilled on whether she was involved in creating malicious websites attacking Ms Ghost that referenced the alleged complaint.
Wilson has been accused of directing a crisis PR team to create the websites, but denies any involvement.
12°C