The Celebrity Big Brother contestant voiced her disapproval of the 'Toxic' singer's appearance at an official announcement of her X Factor USA judging role last week.
Writing in her OK column, Katona joked: "Britney Spears is The X Factor's new face - but she looks like she should be in The Only Way Is Essex.
"Normally judges look immaculate, but then she's had a tough few years. I'm not sure how she'll go down on TV. Her figure is great, but she just needs a new make-up artist and some acrylic nails - and that fake tan needs a good scrub."
However, Katona said that she is "rooting" for Spears and fellow new judge Demi Lovato after their past troubles.
"Demi has admitted to having problems and her and Britney Spears have both got lost in life as I have, so I'm rooting for them both," she wrote. "It's a good chance for them to prove themselves."
Katona recently revealed that she often gets called "the British version of Britney", but admitted: "I don't know why... at least I never shaved my head."
Spears reportedly landed $15m (£9.5m) to judge The X Factor USA.