Or maybe she is avoiding people judging her for being overweight? If she was normal weight for her height, she wouldn't be so defensive.
I find it funny to see how people are always against revealing any sort of information if they are not in shape/fat/overweight/obese. If they were fit, they would have no issue revealing this information. You never see a fit person get defensive, and they try to let people know once they become fit how much they were, how much they are now, how tall they are to put it in perspective, and how much they can lift.