Christ wasn’t under the curse of original sin because he wasn’t conceived naturally. He was conceived of the Holy Spirit, so he was sinless.
Your point about “Well, then, why can’t He apply the merits of the Cross to His mother *before* Calvary? Does God live in time? What does “before” and “after” mean to Him?” wouldn’t have any impact on her supposed sinlessness. The merits of the Cross remove the penalty of sin from a believer, but that doesn’t mean a believer will never sin again. Paul makes it clear that a believer still has the flesh nature within them that is at war with the Holy Spirit.
So, even if God said that Mary was redeemed before the Cross as you say, that wouldn’t mean that Mary never sinned.
It takes two to conceive, no? Are you asserting that Christ took no flesh from His mother?
So, even if God said that Mary was redeemed before the Cross as you say, that wouldn’t mean that Mary never sinned.
Hmm. I get your thinking, and I should have been more careful in my language. The work of the Cross involves two things: justification and sanctification. I, and most Catholics actually, consider the two of them together as the work of Redemption.
So Christ not only removes the penalty of sin (justification), he gradually makes us holy (sanctification/theosis). I am applying both of these to Mary when I am talking about the merits of Calvary. If she was perfected in grace, then she was both justified and sanctified, which meant she could not sin again, just as we will not sin again in heaven.