If you want to say the Lord did not have a physical appearance prior to Mary, then you negate all the physical descriptions of the Lord throughout the Old Testament.
People obviously ate and drank with Christ prior to the Incarnation so that can't be right. However, no one that I know of run around with sapphires under their toes. Of course I might be running with the wrong crowd.
At the risk of minimizing the Incarnation, the only thing that happened was our Lord Jesus took on the form of us, identifying Himself physically with His creatures. Still God, but now man. How precisely He did this is a mystery but He chose to do it through a virgin; a virgin who needed a Savior just like everyone else for we all have sinned and fall short. Mary and Joseph didn't even have a chose in naming Him.
Now why you would like to believe Mary was sinless I don't know. Our Lord Jesus chose to be thrown into a fithy, vile, corrupt environment for 33 years; tempted in every way (probably more) than we are, yet without sin. Why Catholics think Mary had to be a pure environment so that our Lord Jesus could come into this world is the real mystery.
What do you mean by the "Mother of God"?
No, it would be saying that God the Word Incarnate did not.
What do you mean by the "Mother of God"?
I mean to be clear about the fundamental tenets of our faith. Who Jesus is is inherently connected with who Mary is and their relationship defines the Incarnation.
By "Mother of God," I mean that Jesus was God Incarnate, begotten not made, one in Being with the Father - Who by the power of the Holy Spirit was born of the Virgin Mary.