Are you saying that if Mary had rejected the "choice" to bear the Messiah, she would have remained sinless? Would she then have gone to heaven anyway because she didn't need a savior? 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? 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?
“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.