She told Ryan Seacrest's 102.7 KIIS FM show: "Yes, it's something that I would have loved to do, actually. But our schedule doesn't allow and it's a demanding schedule to be on that show.
Judges on the show have to go from city to city deciding which singers will go through to the next stage of the competition, then act as mentor to a number of acts and judge the live TV show on a weekly basis.
So far only Simon Cowell and music industry executive L.A. Reid have been confirmed for the panel.
Other stars linked to the show have included Cheryl Cole - who stars on the UK version of the programme ' Nicole Scherzinger, Jessica Simpson and Katy Perry.
Simon has admitted to having sleepless nights over the final line up, saying: "The truth is that the reason we haven't announced the panel yet is that nobody can agree.
"You make a decision, then you get nervous about it, then you wake up in the middle of the night saying, 'I've made a terrible mistake.' You call everybody the following day to say you've changed your mind and then 24 hours later you go through the same process again.'
Meanwhile, preliminary auditions have been held in Los Angeles, Miami and New York.