She did have free will and she wouldn't have said 'no' because she wasn't asked. But either had to say, I don't accept the Word given to me or say, “Behold, I am the servant of the Lord; let it be to me according to Your Word.”
Those who don't serve The Lord - God's Word is NOT their final authority. God's Word was the final authority for Mary as Scripture clearly shows as she saw herself as His servant. There was no 'think about it' from the angel or 'Let me think about it first' from Mary. Her heart had already been committed to The Lord.
If the mother of Jesus gave something to the nature of God, then she must be coeternal with God.
Not good to lean unto your own understanding; it will led to error. "As the heavens are higher than the earth, so are My ways higher than your ways and My thoughts than your thoughts." Isaiah 55:9
However, following your questioning and comment - since mothers gave birth to the presidents we had - why aren't they called co-presidents? Geez, they don't even make it to VP and never have. And that is in the natural/worldly - where anything goes - and no one considers it to be true. Now we are talking about SUPERNATURAL and you seem OK with it? Rome truly duped catholics, their minds are mush while not having a clue how the SUPERNATURAL works.
Yet Jesus tells us - His mother and brothers are just like anyone who 'hears and obeys' God's will. It's the opposite of how the 'world' views mothers, brothers and sisters. And Catholicism is in the world view.
Worldly man-made teachings vs. God's Holy Spirit inspired WORD - who are you going to BELIEVE? There are two choices, choose one because you can't serve two masters.
I can just hear the women now; as they gather at the well...
"MY son is going to be a doctor and make LOTS of money!"
"Humph! MY precious son is going to be a LAWYER and help your doctor son KEEP his money!"
"Gosh... MY son is going to be the Son of GOD."