The Superstar singer had recently labelled Leona a "poor man's Mariah Carey" and argued that as the winner of a TV talent show, she would "fade into obscurity eventually".
Though Jamelia later denied making the comments, Leona has refused to be drawn into a public slanging match.
"I don't know if she did say it. If she did, it's a shame, because The Feeling's not mutual," Leona told Celebs on Sunday. "I think she's great.
"It's quite hurtful to hear that. As female artists we shouldn't be bitching about each other, we should be supporting each other."
She continued: "There are so many great young female artists - Kate Nash, Katie Melua, KT Tunstall.
"Amy Winehouse is a great performer and I know she's been through some difficult times, but people should focus on her music instead."
The 22-year-old X-Factor winner easily outsold the competition to grab the number on spot yesterday, holding off the challenge of Take That and McFly to reportedly seal the biggest singles sales of the year so far.
Leona's mentor, X-Factor judge Simon Cowell, told the BBC: "The sales are incredible. I'm absolutely thrilled for Leona, she thoroughly deserves it."