Until a male doctor came (in the mid of the 90's) the "Overseer" was a guy from the adminstration-department.
Under American licensure law, that would be illegal. A professional cannot be subordinate to a non-professional in matters of expertise/practice. Of course, I doubt the WT cares about such trivialities of Caesar's law and has some way of getting around it, in case anyone checked. But it, in theory, could raise interesting questions--if the non-prof brother wanted things done a certain way, the professional sister would be jeopardizing her license to go along with it, if it was not in the best interests of a patient or the medical practice.
Stupid hierarchy.