AMy niece is wanting a cake covered in glitter and done in an ombré effect of white descending gradient to pink. At thought on how to do this and look good? The only idea I can think of is to cover the cake in white sanding sugar and then use airbrush to achieve the coloring. But can you airbrush the sanding sugars?

AIf you don't soak them, I don't see why not. Just test it, swipe some buttercream on a cake board, stick some sanding sugar to it, and very, very lightly airbrush it. Let it dry an hour and go back to see if there is anything left of it! If there is, add your second coat. Wait another hour, repeat.