I had this problem as a child also - it eventually just went away on its own as I grew. I know I did have athlete's foot twice (I believe) and treated it with over-the-counter powder. You could see a dr if you want, but probably not totally necessary....maybe just bring it up at her yearly physical. Does it seem to bother her?
Mine was most likely eczema also. I don't remember ever going to the dr and getting a diagnosis for it. It was kind of annoying, but never hurt and, as I said, went away on its own eventually...
I wouldn't worry too much....especially if it is not bothering her. Maybe try some of that OTC foot powder just to see if it works...
PS... my son also had eczema as a baby and we had to occasionally apply "steriod" cream - it is just cortizone 10 ointment...not a big deal. Again, over-the-counter and a very low dose of "steriods"..but it does seem to clear up most eczema spots.