Toni Braxton is being stalked by an obsessed fan so insistent that the situation has affected her daily life and that of the Broadway musical Beauty and the Beast, in which she stars. In response to a bombardment of threatening e-mails and letters, the singer - who plays Belle in the show - wears a disguise when leaving the theater, leaves with a security guard by the front doors used by theatergoers, has reduced her performances from eight to seven a week, and no longer signs autographs for fans. Said a source close to the show: ``She's like a prisoner. She has to look over her shoulder wherever she goes. . . . The Disney people are very concerned about it.'' There's a possible plan of putting metal detectors in the theater. As it is, undercover security people eyeball theatergoers as they arrive. Deborah Gibson, who also played Belle, was stalked earlier this year. Michael Folkner was charged in that instance, and his case is pending. Stewart Lane, co-owner of the theater where Beauty is playing, said only: ``The theater is taking every precaution necessary to ensure the safety of the cast and the audience.''