Again, it would depend on how much of the song was used. Let's say, there was this leftist band that sang a song played on Rush Limbaugh's show (BTW, there is), so long as he played only a portion of the song he could continue to use it as his bumper music without having to pay royalties. The same would be true for Michelle. It depends on how much of the song she used.
In this case it is likely that Tom has the right to tell her to quit using his song, especially if she used more than a small portion of the song at introduction, however it isn't an absolute right, it depends on exactly how much of the song is used.
You'll see this in usage on American Idol often, they'll allow their singers to sing only a portion of a song, and they know exactly how much can be used without permission, believe me. When a full song is used they need to get permission, they usually refuse to pay for that until near the end of the show... Hence you'll get portions played, but not full songs unless it is from a list of "free use" songs where the copyright is free, until the show reaches the point where the audience is voting and where they deem it worth the cost to pay the royalties.
