"Was Mary the mother of the Godhead?"
You're coming a little late to that discussion, Dr.E, about 2500 posts too late. Frankly, to anyone with even a simple grasp of Trinitarian theology, the question is silly.The simple answer is NO. The Theotokos gave birth to the enhypostatically conceived Incarnate Word. You really should have read +Athanasius on the Incarnation at the link I posted. But if not him, then try any one of the Cappadocian Fathers or even +Gregory Palamas. For that matter, read Luther.
As has been said, 2500 posts ago and probably yesterday, to believe that Mary remained a virgin is not the same thing (and indeed light years away) from the heresy that purports Mary to be "sinless."