I belive her tbh,
Simon is an j*rk, I mean he fired Cheryl and looked for the easy route and hired Nicole, she probably got a one season contract to see if she could fill in the part, since the show viewings dissapointed, they didn't asked her back. Paula and Steve probably were fired to refresh the series, since they didn't had anything to loose and needed to gain viewers this next season, that is why they hired Britney and Demi. Demi for the pre-teen and teen viewers and Britney for the overall viewers.
If Nicole really was so bad, Simon would have never pushed her to the UK, since there were loads of other options there.