Complex sentence: McCartney had no problem with the parody, but because "Free as a Bird" was written by John Lennon, McCartney turned the decision over to Yoko Ono, who denied permission, because she was uncomfortable with the parody idea.
Split into simpler sentences: McCartney had no problem with the parody, but because "Free as a Bird" was written by John Lennon, McCartney turned the decision over to Yoko Ono. She denied permission, however, because she was uncomfortable with the parody idea.