The 21-year-old singer, who topped the charts earlier this month with single R.I.P, will join Gary Barlow, Tulisa and Louis Walsh at the O2 Arena this afternoon.
And TellyMix will also be there, bringing you all the latest gossip from the auditions.
Sources have said that boss Simon Cowell is after breakthrough artist Rita to join the panel full time, so we're looking forward to see how she handles her 'trial'!
“It’s hers to lose. If she does well as a guest judge on Monday, she’s got a real chance of getting the job,” a source told the Daily Star Sunday yesterday.
The supposed insider added: “Bosses have been hugely impressed by her in meetings and they feel she has an amazing future."
Rita will follow Geri Halliwell and Leona Lewis, who have both sat on the panel so far this year.
A new permanent judge is expected to be announced in time for the bootcamp stages in the summer.
[cat]The X Factor 2012[/cat] will air on ITV1 this autumn.