Newly married Kelly sailed through to the next round of the competition last Sunday – even if Corr (41) wasn't impressed with her performance.
Sharon argued that fans of the show are voting for Kelly, who is eight months pregnant, for all the wrong reasons.
"We have teams behind certain artists and sometimes it's not merited," she said. "Like counties behind certain singers just because they are from their county and I find that very difficult, because it ends with people out of the competition that shouldn't be out."
"Kelly didn't give a great performance. I couldn't hear her."
But protective mentor Kian told the Herald that it is unfair and unnecessary for Sharon to single Kelly out.
"I really dislike the way Sharon picked on Kelly," he said.
"Hers wasn't the worst performance of the people who topped the poll on the night and I can't understand why Sharon would single her out."
Kian says it is especially harsh, given that Kelly is so heavily pregnant.
"At the end of the day she is an 18-year-old, eight months pregnant girl and it was her first time to appear on live television," he said.
And former Westlife star Kian has tipped the newlywed to win the show.
"She could win the whole thing , there is a huge amount of interest in her."
Kelly sang Leona Lewis's hit A Moment Like This last weekend and sailed through the live show. Kian congratulated her – "In your circumstances it's a nerve-wracking situation."
But Sharon was less enthusiastic in her praise. "You did struggle with the high notes, it's a brave song to do and hard to deliver."
After the performance Kelly admitted she had found the live show slightly overwhelming, though she scored the highest in Team Kian.