The full Godhead right?
Colossians 2:9 For in him dwelleth all the fulness of the Godhead bodily.
So Mary was the mother of the Father, Son, and Holy Spirit? Is that what you are saying?
No, that is not what I am saying. Mary conceived and gave birth to the Second person of the Trinity. She did not conceive and give birth to the Holy Spirit, who came over her. And she did not conceive and give birth to the Most High, who overshadowed her.
Mary can rightly be called the mother of God because Jesus is God, whole and entire, just as the Father and the Holy Spirit are God, whole and entire. They are one God, of one substance, essence, and nature.
Yet they are distinct in their relations with one another. They work as a single operation in all three persons, with each showing forth what is proper to him in the Trinity. This can be seen in John 14, where Jesus tells His disciples that He is in the Father and the Father is in Him, and that the Father who dwells in Him is doing His works. Then He says He is going to the Father, and that He will ask the Father to send another Advocate, the Spirit of truth, who will teach them everything and remind them of all that Jesus told them. The Father, Son, and Spirit, working as one, but each working in what is proper to him.
It was proper for Mary to be the mother of God the Son, but not to be the mother of the Father or the Spirit.