An artist should always be the one who determines the content of their work. If an artist wishes to only photograph children holding red balloons, and not blue ones, so be it. If she wishes to photograph exclusively traditional weddings- it's her artwork! I am a portrait painter, and I have declined several commissions in the past, such as when the person insists their dog must be in the painting. I shouldn't be forced (neither by the potential customer, nor by the court) to waste my time doing artwork that that doesn't suit my personal taste.