Prom/Formal Dress by Camille la Vie Size 8 in Grey & Silver

My daughter wore the grey dress in the photos to prom. The tag says size 8 but I believe the dress fits more like a size 4 and am guessing it was sized incorrectly. It measures about 15 inches across at the waist, the armholes are 8 inches. It is longer in the back, measuring about 70 inches from the shoulder to the back, and about 62 inches from the shoulder to the middle front.