REI Beautiful Blue Woman's Hiking‎ Shirt size Medium or Large

Woman's hiking/fishing shirt in beautiful blue. Zipper vents, wider collar, and large pockets. Light turquoise color. UPF 30+. Smoke free home, no rips or stains. Measure are pit to pit 22", length is 27", pit to end of sleeve is 19". No size tag that is readable. I would guess this to be a medium or large.