Price, who sparked controversy earlier this month after calling Brook a "heffer" in her column, allegedly responded to news of the ex-couple's reconciliation by sending the rugby player messages mocking his bedroom prowess.
"When she discovered he was back with Kelly all over again, Katie flipped out and sent Danny a series of angry messages, telling him that he was 's**t in bed'," a source told Now.
"Her last text to him was along the lines of, 'Good luck with Kelly because she'll only dump you as soon as she gets bored again'."
Another source claimed that Price, who is expecting her fourth child with third husband Kieran Hayler, has become "obsessed" with Brook, allegedly spending hours comparing images of herself and the Celebrity Juice star on Google.
"She's always been jealous of Kelly and is constantly scrutinising her looks, who she's hanging out with and the way she dresses," the insider claimed.
"It's sad because deep down she knows Kelly's better looking than her."
A representative for Price told the publication: "Katie isn't in contact with Danny, but wishes him well with any relationship he chooses to have.
"It's completely unture that Katie's been looking at pictures of Kelly online or comparing herself to Kelly.
"Physically Kelly and Katie are very different, but there's no doubting that Kelly is very beautiful."
Price has yet to address the claims directly, but may have been referencing the story when she tweeted this afternoon (February 26): "now now yawn x"
Brook responded to the "heffer" comment by describing Price as "unladylike" and rude, prompting the glamour model-turned-businesswoman to accuse her of exploiting the controversy to sell underwear.
However, Brook did insist that she has "no issue" with Price over her romantic history with Cipriani.