Vintage (handmade?) Dress, Sz 12

This is a vintage dress that could possibly be handmade. There are threads around a lot of the seams, but stitching is strong and no gaps or holes anywhere that I can see. Side zipper under the arm is definitely old. Has one pocket. Pit to pit around 21 inches, waist at smallest is about 17 inches, and from waist to hem is just shy of 26 inches. There also looks to be a small ironing mark at the waist, but not noticeable unless you look for it (reference last picture)..