Moonlight is very soft and has a bluish tint, which you captured nicely. Accurate shading has a full range of tone: highlights, midtones, and shadows. You really only have the first two. To give the character more depth, add dark blue shadows under her head, on the bottom half of her breasts, and at the creases of her knees. Also, the longer purple part of her skirt would be very dark, because there's almost no light hitting it.