BTW: That question has absolutely nothing to do with whether the syllogism is formally valid.
It is remarkable how many people there are who refuse to answer a yes-or-no question.
As stated the syllogism is valid. The invalid comes when Catholics try to conflate that syllogism with the birth of Jesus, claiming Mary is the Mother of God. And you know that yet persist in trying to confuse the issue. My question points at the heart of the deception to which your syllogism was aimed for effect. Sally gave birth to a fireman? No she gave birth to a baby whio later became a fireman. Did Jesus later become God? No, you say. Then Jesus was conceived as a human embryo and grew to birth age then grew into manhood ... as a human who was in The Father and the The Father in Him. Mary is the Mother of Jesus, but since Jesus IS The Word made flesh, He existed before Mary was even conceived. Mary is not the mother of someone Who existed before she was created. She is the Blessed mother of the body and man called Jesus.