Ave Maria
You need to brush up on your Roman Catholic christology. Mary is called, “Theotokos,” or “Mother of God” (more literally, “One who gave childbirth to God”) by the Catholic Church specifically to emphasize the fact that Jesus was fully human in every way, even though he was also fully divine. This is to clarify and expand upon Luke 1:43, where St. Elizabeth calls the Blessed Virgin Mary, “Mother of my Lord” (here, the translation is closer to simply, “mother of my lord.”); Whereas Luke 1:43 might be taken in any of a variety of ways (”Mama of my Lord,” “Maternal guardian of my Lord,” “Legal mother of my Lord,”), the title Theotokos was chosen to emphasize the biological aspect of “mother”; that Mary wasn’t simply “mother” in some limited sense, but in the most complete sense possible.
As Cyril of Alexandria explained to Nestorius at the infallible Ecumenical Council of Ephesus, “the holy fathers... have ventured to call the holy Virgin Theotokos, not as though the nature of the Word or his divinity received the beginning of their existence from the holy Virgin, but because from her was born his holy body, rationally endowed with a soul, with which body the Word was united according to the hypostasis, and is said to have been begotten according to the flesh...
...Confessing the Word to be united with the flesh according to the hypostasis, we worship one Son and Lord, Jesus Christ. We do not divide him into parts and separate man and God as though they were united with each other [only] through a unity of dignity and authority... nor do we name separately Christ the Word from God, and in similar fashion, separately, another Christ from the woman, but we know only one Christ, the Word from God the Father with his own flesh... But we do not say that the Word from God dwelt as in an ordinary human born of the holy virgin... we understand that, when he became flesh, not in the same way as he is said to dwell among the saints do we distinguish the manner of the indwelling; but he was united by nature and not turned into flesh... There is, then, one Christ and Son and Lord, not with the sort of conjunction that a human being might have with God as in a unity of dignity or authority; for equality of honor does not unite natures. For Peter and John were equal to each other in honor, both of them being apostles and holy disciples, but the two were not one. Nor do we understand the manner of conjunction to be one of juxtaposition, for this is insufficient in regard to natural union.... Rather we reject the term ‘conjunction’ as being inadequate to express the union... [T]he holy virgin gave birth in the flesh to God united with the flesh according to hypostasis, for that reason we call her Theotokos... If anyone does not confess that Emmanuel is, in truth, God, and therefore that the holy virgin is Theotokos (for she bore in a fleshly manner the Word from God become flesh), let him be anathema.
(”Anathema”, here, means, roughly, “excommunicated”; “Hypostasis” means, roughly, “unified in one substance”: “Hypo” meaning “under,” and “stasis” meaning “state”; Hence, “hypostasis” is the “underlying state.”)