Avatar olive green long dress with black/ dark green underlay. Size S/M NWT

Avatar long, Olive green dress with black and dark green striped underlay. Gathered skirt in the front and back. Unique sleeves. Unique dress! NWT. Size S/M. Pit to pit measures 18 inches and length is 51.5 inches. 100% cotton. To figure out the size for you look at the measurements. Hard to tell if small or medium.