Rooney, who is married to England's record scorer Wayne Rooney, posted a tweet in which she revealed how she came to suspect Vardy, who denies any wrongdoing.
In the message, she said Vardy – wife of Leicester City's Jamie Vardy – held the only account that had access to her Instagram stories.
Rooney said she had removed access to all users except Rebekah Vardy, and alleged a series of "false" stories that she posted on there found their way to UK tabloid The Sun.
Rebekah Vardy responded by tweeting a lengthy message to Coleen Rooney, who she claimed to have discussed the matter with on the phone, to reject the claim.
"This has been a burden in my life for a few years now and finally I have got to the bottom of it……" Coleen Rooney tweeted, along with an image of a longer statement.
Coleen Rooney's statement read: "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.
"There has been so much information given to them about me, my friends and my family – all without my permission or knowledge.
"After a long time of trying to figure out who it could be, for various reasons, I had a suspicion.
"To try and prove this I came up with an idea. I blocked everyone from viewing my Instagram stories except ONE account. (Those on my private account must have been wondering why I haven't had stories on there for a while.)
"Over the past five months I have posted a series of false stories to see if they made their way into the Sun newspaper. And you know what, they did! The story about gender selection in Mexico, the story about returning to TV and then the latest story about the basement flooding in my new house.
"It's been tough keeping it to myself and not making any comment at all, especially when the stories have been leaked, however I had to. Now I know for certain which account/individual it's come from.
"I have saved and screenshotted all the original stories which clearly show just one person has viewed them.
"It's………. Rebekah Vardy's account."
In a tweeted reply, Rebekah Vardy said she had never passed on such information – despite claiming to have been approached to do so by journalists.
She blamed "various people having access to my insta" and was "disgusted" to have to deny involvement at a time when she was "heavily pregnant".
"As I have just said to you on the phone, I wish you had called me if you thought this," Rebekah Vardy's statement read.
"I never speak to anyone about you as various journalists who have asked me to over the years can vouch for.
"If you thought this was happening you could have told me & I could have changed my passwords to see if it stopped.
"Over the years various people have had access to my insta and just this week I found I was following people I didn't know and have never followed myself.
"I'm not being funny but I don't need the money, what would I gain from selling stories on you?
"I liked you a lot Coleen & I'm upset you have chosen to do this, especially when I'm heavily pregnant. I'm disgusted that I'm even having to deny this.
"You should have called me the first time this happened."
Rooney, who is also Manchester United's record goalscorer, will return to English football following his time with MLS team DC United when he joins Championship club Derby County in January.
Vardy has scored five Premier League goals for Leicester this season, with Brendan Rodgers' men riding high in fourth position.