Vintage 80's neon Byer Too! floral a-line size Medium?

Outstanding pristine vintage dress by Byer Too! Vibrant floral colors are striking, it's just a lot of gorgeousness in a small feminine package! Tag says size 13 (vintage can run small). The mannequin is a size 4/6, so my best guess is a size 6/8, maybe a junior size 9? Wear to a formal or special occasion such as the prom, or date night, a semi-formal party, a cruise, you name it!