“Are you saying that if Mary had rejected the “choice” to bear the Messiah, she would have remained sinless?”
Yes. God asked. He did not demand.
“Would she then have gone to heaven anyway because she didn’t need a savior?”
She was already saved, by Christ himself.
“If so, would Christ’s redemption not be needed for her since she never sinned because of the graces she had already been given of God?”
Her redemption was already in Christ prior to the atonement. What you mean is that Christ’s atonement on the Cross was unnecessary for her. The two are not quite the same thing. Christ redeemed sinners on the Cross, but not her because she had never sinned.
“If that is the case, as you are sounding like it is, then why couldn’t/wouldn’t God have just done that for ALL mankind and EVERYONE would go to heaven and Jesus wouldn’t have needed to die?”
God *did* in fact do this.
JCB: Yes. God asked. He did not demand.
Luke 1:26-38 26 In the sixth month the angel Gabriel was sent from God to a city of Galilee named Nazareth, 27 to a virgin betrothed to a man whose name was Joseph, of the house of David. And the virgin's name was Mary. 28 And he came to her and said, “Greetings, O favored one, the Lord is with you!” 29 But she was greatly troubled at the saying, and tried to discern what sort of greeting this might be. 30 And the angel said to her, “Do not be afraid, Mary, for you have found favor with God. 31 And behold, you will conceive in your womb and bear a son, and you shall call his name Jesus. 32 He will be great and will be called the Son of the Most High. And the Lord God will give to him the throne of his father David, 33 and he will reign over the house of Jacob forever, and of his kingdom there will be no end.” 34 And Mary said to the angel, “How will this be, since I am a virgin?”
35 And the angel answered her, “The Holy Spirit will come upon you, and the power of the Most High will overshadow you; therefore the child to be born will be called holy—the Son of God. 36 And behold, your relative Elizabeth in her old age has also conceived a son, and this is the sixth month with her who was called barren. 37 For nothing will be impossible with God.” 38 And Mary said, “Behold, I am the servant of the Lord; let it be to me according to your word.” And the angel departed from her.
Apparently Luke neglected to add that bit of information.
Could you point us to the Scripture that tells us that God asked Mary's permission?