Complex sentence: She introduced Marcel Proust and Reynaldo Hahn in the Parisian salons of the aristocracy and hold herself a "salon" where she received the high society in her "hôtel particulier" rue de Monceau.
Split into simpler sentences: She introduced Marcel Proust and Reynaldo Hahn to the Parisian salons of the aristocracy. She herself held a "salon" where she received high society in her "hôtel particulier" on the Rue de Monceau.