I'm suggesting that I don't accept this premise:
For all people P, if P experiences pain in childbirth, then P is sinful.
I think you're getting carried away with your view of the curse in Genesis. In general, Genesis outlines some of the overall brokenness of the fallen human condition: Pain in childbirth, thorns and thistles in the garden, domineering husbands. But I think it's too much to say that all of these apply to each individual person if and only if that person is sinful. For example, I think it's theoretically possible that if Jesus had planted a garden, he might have had weeds in his garden, even though he was sinless, because weeds are something humans in general have to put up with. (I know you've said you don't accept Jesus as an example of a sinless human. Nevertheless, I insist that he does qualify.)
If I accept your premise, then your conclusion follows. But I don't accept your premise.
As to this assertion:
that is the whole question, isn't it? Catholics assert that Mary was protected from Original Sin because of her unique relationship with Jesus. You (and most Protestants) say that she was not protected from Original Sin. Maybe it's better to argue about that point directly, instead of going the route of arguing about pain in childbirth.