Mrs Rooney, 35, accused Mrs Vardy, 39, of leaking "false stories" about her private life in October 2019 after carrying out a months-long "sting operation" which saw her dubbed "Wagatha Christie".
Mrs Rooney then wrote on Instagram and Twitter: "For a few years now someone who I trusted to follow me on my personal Instagram account has been consistently informing The Sun newspaper of my private posts and stories.
"I have saved and screenshotted all the original stories which clearly show just one person has viewed them. It’s………. Rebekah Vardy’s account."
Mrs Vardy, who is married to Leicester City striker Jamie Vardy, denies the accusations and is suing Mrs Rooney for libel.
At a hearing on Friday, Mrs Vardy’s lawyers asked the High Court to throw out parts of Mrs Rooney’s defence, including allegations of Mrs Vardy’s close relationship with The Sun and benefits she received.
Hugh Tomlinson QC, for Mrs Vardy, said: "The purpose of this application is to clear away what we say is a mass of irrelevant or peripheral material to save time and costs."
Mr Tomlinson denied Mrs Vardy wanted those parts of the defence thrown out because they would be embarrassing for her.
"If necessary she will deal with it but we say it is not necessary and will be a waste of everybody’s time," he added.
The barrister argued that the central issue was whether Mrs Vardy was leaking posts from Mrs Rooney’s Instagram and that the other issues would not be necessary.
In his written submissions, Mr Tomlinson said most of the claims made by Mrs Rooney’s lawyers were in dispute and denied.
He continued: "Even if it were established that the claimant has ‘an exceptionally close relationship’ with The Sun, that it gave her positive coverage, that she has a history of self-promotion or is the ‘Secret Wag’, does not mean that it is more likely than not that the claimant had regularly informed The Sun about the defendant’s private posts.”
He added: "Most of the factual allegations which are made are, in fact, wrong, but considerable time and costs will be wasted in examining them… It will be a monumental waste of time and costs."
The move to throw out part of the defence was opposed by Mrs Rooney, with her barrister David Sherborne arguing that the "exceptionally close relationship" Mrs Vardy is said to have had with The Sun is a key part of the case.
In written submissions, Mr Sherborne said Mrs Vardy had a "habitual practice" of providing private information to the press to promote her profile.
He said: "The timing of positive coverage of the claimant in The Sun was strikingly close to the publication of other articles … that were leaked from the defendant’s private Instagram.
"This supports the inference that the claimant was benefiting from the leak of private information about the defendant to the newspaper."
Mr Sherborne added that Mrs Vardy used her close relationship with The Sun or its journalists "for the purposes of promoting or financially exploiting her public profile".
The barrister later claimed Mrs Vardy would receive a split of commission and revenue for stories given to The Sun through the Front Row Partnership, a PR agency where Mrs Vardy was a client.
Mrs Vardy has denied any knowledge or authorisation of passing on private information.
On Friday, the High Court also heard that mediation took place between Mrs Vardy and Mrs Rooney, but was unsuccessful.
Mrs Vardy has also applied for summary judgment – a legal step which would see that part of the case resolved without a trial – in relation to Mrs Rooney’s claim that Mrs Vardy leaked a story to The Sun about her returning to TV presenting.
Mrs Rooney said she blocked everyone except Mrs Vardy from seeing her Instagram stories between September 1 and October 4 2019 before posting a selfie with text reading "easing my way back into work!! TV decisions today" on September 25.
A story reporting her desire to revive her TV career appeared on The Sun’s website three days later, Mrs Rooney claims.
However, Mrs Rooney said she "invented" the story as part of her investigation to discover the source of the leaks and had no intention of entering into more television work.
Mrs Rooney has also said she planted stories about her travelling to Mexico to "see what this gender selection is all about" and the basement flooding in her new house.
Mrs Vardy sued Mrs Rooney last June, claiming she "suffered extreme distress, hurt, anxiety and embarrassment as a result of the publication of the post and the events which followed".
In her written case against Mrs Rooney, Mrs Vardy’s lawyers said the abuse she received made her "feel suicidal", adding: "She suffered from severe panic attacks and anxiety which manifested in being scared to leave her house."
Mrs Vardy claimed her husband Jamie was targeted during football matches, with opposition fans chanting "your wife is a grass" for up to five minutes at a time.
The hearing before Mrs Justice Steyn continues.