[count-your-change]

It was I who misunderstood your comment. I too will try again.
If the Son of God, Second Person of the Trinity was such even before Mary existed then in what sense is Mary mother to God, Second Person of the Trinity?

[Deo volente]

In the sense that He continues to be the Second Person of the Trinity FROM THE INSTANT He was Incarnate in the womb of the Virgin Mary, who became His Mother at that very instant.

Mary did not pre-exist the Second Person of the Trinity. She is, after all, a creature and had a beginning in time, like all creatures. But she BECAME HIS MOTHER when HE BECAME INCARNATE in her womb. He is ONE PERSON, but now also with a human nature. He is not two persons, however. The two natures are united in one Divine Person from the moment of the Incarnation onward.

Nestorianism is a denial of this truth.