What credentials does she have that qualify her to be a judge ? What has she ever done ?, apart from having a toilet mouth ?
She's Ozzy's manager, and whether you like him/heavy-metal or not, she managed to turn a guy who nobody thought would even survive outside of Black Sabbath into a huge solo artist in his own right.
It is one of those tough questions but nobody can really say whether Ozzy would have been as successful as a solo artist had it not been for Mrs. O's very shrewd dealings and marketing.
In short, she knows what it takes to make somebody a star and is FAR more qualified to be a judge than someone like Danni Minogue or Nicole.