Writing in her weekly The Sun column, controversial Katie blasted Gemma's decision to walk out of the Australian jungle after just three days, saying she blew her chance to change public perception of her.
"Gemma had the perfect platform to show everyone who criticises her that she was strong," wrote Katie.
"She was offered all the camera time in the world and a fee! To show us what she was made of… But she didn't. Instead, she took the easy option and sulked, stropped and cried her way through three days (in Gemma speak, free days) bringing everyone else down with her.
Katie, who found fame as an Apprentice candidate, went on to say that "Z-list celebrities aren't expected to do much" but "Gemma has failed to meet this requirement."
"She is the worst of reality excess, mainly because she let us down, and, most importantly, let herself down. Of course, her agent will scrabble about finding excuses – a horrible break-up, her mum's illness, her imagined malaria. Perhaps a loss in Craig Charles's family will help give her some perspective."
Just one day after Gemma quit the jungle, Coronation Street actor Craig withdrew following the sudden death of his brother back home in England.
Katie wrote: "Be clear, Gemma just wasn't up to the job and to all of those working long shifts in jobs you hate, I am sorry."
She concluded this week's column with the words: "I don't deserve celebrity, get me out of here."
Gemma is now back in the UK after leaving Brisbane International Airport on Wednesday.
Reveal is now on Google Plus! Join us here for the latest pictures, fashion and celebrity news!