She's got the big voice, and now Tamera Foster has been accused of having an attitude to match, according to ' X Factor ' insiders. The 16-year-old singing hopeful is reportedly a 'nightmare' to work with over the top diva demands who causes conflict behind-the-scenes. Tamera Foster A source told Reveal magazine: "Tamera is a great singer with good looks, but boy, does she know it. "She's over ...