But God did not do any such manipulation with Mary: she was actually pregnant with her own baby. You have just invented something not in the gospel. If God did not want Mary to play the role she played, He could have incarnated Jesus the way He made Adam from essentially nothing.
Further, Mary appears several times throughout the gospels, at pivotal points of Jesus’s ministry; this is not consistent with your “vessel” theory.
Matthew 00020 1:20 But while he thought on these things, behold, the angel of the Lord appeared unto him in a dream, saying, Joseph, thou son of David, fear not to take unto thee Mary thy wife: for that which is conceived in her is of the Holy Ghost.
Luke 00024 1:24 And after those days his wife Elisabeth conceived, and hid herself five months, saying,
If you will notice it says that the Holy Spirit conceived when speaking of Jesus but when speaking of John the word say that Elisabeth conceived.
As far as the pivotal time this is what Jesus had to say about her meddling,
2:2 And both Jesus was called, and his disciples, to the marriage. 00054 2:3 And when they wanted wine, the mother of Jesus saith unto him, They have no wine. 00055 2:4 Jesus saith unto her, Woman, what have I to do with thee? mine hour is not yet come. 00056 2:5 His mother saith unto the servants, Whatsoever he saith unto you, do it.
If you will notice He did not even caller Mother but WOMAN.