Unless she is really good at eying measurements or had a ruler handy to be sure she’s not going to know the difference in a couple of inches one way or the other.
No we don’t have measuring down to a science just eying it. Even so we still get asked what size is the best.
Well some do. When me and my girlfriend first had this conversation I asked her about how she knew the size and she proceeded to tell me the length of her hand from the base to the tip of her middle finger.