"She is a singer at the Paris Opera."
Translation:Elle est chanteuse à l'Opéra de Paris.
not sure if the reason that it is a certain building is crucial here....As in New York too it is a certain building. Thus it would be L'opera de New York' with that logic, I think. Maybe someone else could time in here and give detailed explanation when 'de' and when 'a' for places where consistently cultural events of the same kind happen (like for example there are also theatres with names, famous, and that have the city of their location attached to them, for example Schauspielhaus Hamburg. So would that be 'Schauspielhaus de Hamburg', or 'Schauspielhaus a Hamburg'.?