The 27-year-old singer has been a judge on the UK talent show for three series now but admitted she wasn't keen on the job at first.
She said to Britain's X magazine: 'Well, when Simon first asked me to do The X Factor, I said: 'Never for all the tea in China will I do The X Factor.'
'That's exactly the words I said to him, and he went: 'You will, and I'll see you in a year's time.' And I really didn't want to do it.'
Asked why, she added: 'I didn't want to be the person that stops people and says: 'No, you can't.' But then I realised that the people I do put through, I can really help them.'