Want know how to spot a fake blond?
When in doubt, check the eyebrows. Natural blonds do not have super-black eyebrows. Another good example, besides this knock-off Sabrina, is Delinda from the show "Las Vegas." She too had super-black eyebrows, indicating she wasn't any more a real blond than Kiernan here.
Smarter women have their eyebrows lightened if they want to have a prayer of looking even remotely like a real blond, as well as having a professional dye their hair so it looks more natural. Too often I've seen crappy blond hair dye jobs involving making the person's hair too bright and uniform across their head, and the black roots look horrible when the real dark hair grows out.