Mrs Rooney, married to former England star Wayne Rooney, is being sued for libel by Mrs Vardy, who is the wife of Sheffield-born footballer Jamie Vardy, who plays for Leicester City.
It stems from an accusation Mrs Rooney made against Mrs Vardy on Twitter in 2019.
Mrs Rooney claimed that Mrs Vardy had leaked information from her private Instagram page to the press.
She was dubbed “Wagatha Christie” as she detailed how she came about her conclusion.
In a viral social media post in October 2019, Mrs Rooney, 36, said she had carried out a “sting operation” and accused Mrs Vardy, 40, of leaking “false stories” about her private life to the press.
Mrs Vardy denies leaking stories to the media and is suing Mrs Rooney for libel, while Mrs Rooney is defending the claim on the basis her post was “substantially true” and in the public interest.
The fake stories Mrs Rooney planted on her Instagram during the sting operation featured her travelling to Mexico for a “gender selection” procedure, her planning to return to TV and the basement flooding at her home.
In the post on Instagram, Twitter and Facebook, she wrote: “I have saved and screenshotted all the original stories which clearly show just one person has viewed them.
“It's .......... Rebekah Vardy's account.”
On the fourth day of the trial today, Mrs Vardy is due to finish her evidence, with Mrs Rooney then taking her place in the witness box in Court 13 of the Royal Courts of Justice.
The WAG is half English and half Portuguese, as her Dad, Carlos Miranda, was born in Madeira.
She is predominantly known for being a model, and being married to footballer Jamie, whom she married in 2016.
After being released by Sheffield Wednesday at the age of 16, Jamie began his senior career with Stocksbridge Park Steels, breaking into the first team in 2007 and spending three seasons there before joining Northern Premier League club FC Halifax Town in 2010.