It's Christianity 101 which papists have flunked.
Saying “She is the parent of Christ’s humanity” is very much of the essence of the Nestorian heresy, as you would see if you took the time to read up on it.
She is the mother of the whole Jesus, the mother of His Person, the mother of Him. He is one Person, with the Divine and human natures united from the moment of His conception in her womb. He is God, and she is His Mother, from that moment onward.
Simple as that.