Good choice! The Marais is certainly the area of Paris in which I have smelled the most numerous niche-perfume trails.
She is not the only one to have recently decided to locate her perfumery there (see Diptyque, The Different Company) which makes that quarter even more one of the must-perfume-circuits-to-tour for perfumistas.
Boutique du Marais
26, rue de Poitou
Tel: 01 42 24 07 99