Bought this for my fiancee who is newer to riding. The very next ride, she got panicky on loose gravel, and probably locked the rear while grabbing a big handful of front... And went down on her side. Shoulder protector took a little abuse, but her shoulder didn't!
I got her a size small, but it's still a little big for her, and the straps can slide off either shoulder if she doesn't shrug it back in place once in a while. She is pretty small though, about 5'4" and 117lbs... Probably could have gotten her a youth size. She says it's not uncomfortable, and has some room for the "ladies".