hormonal balances would effect more along the lines of facial hair, or pubic hair. legs and arms is genetics. my daughter was so hairy as a baby, shoulders and back. she still is. the 2nd one is not hairy on the shoulder or back, but only on her very lower back. its genetics. think of it like this, the mom has seen her daughter naked her whole life, so either the pedi has seen it himself from all the well visits, or the mother would have noticed a sudden change and took her to the pedi, kwim.
i would be totally offended if someone else mentioned to me that i should have something like that checked out. first i would be upset that you were picking out a physical characteristic of my child that YOU are viewing as a flaw. secondly, i would be insulted that you would think me not competant enough to decide when to seek medical assistance. its one of those things that you dont want to risk, she may be ok with it, but what if shes not.
i dont know what normal is but i dont think what you describe is not normal.