What we have from all this is that Mary was ritualistically impure "according to the Law of Moses" and obeyed the law. You may infer that she also experienced the pains of chidlbirth, although that is not stated int he scripture. None of that points to personal sin, -- that is sin committed by the will of the sinner, -- or to subsequent sexual activity.
"None of that points to personal sin, -- that is sin committed by the will of the sinner, -- or to subsequent sexual activity."
That all comes from her own admission that she needed a savior and the testimony of the Apostles and Luke that she had other sons, James and Jude.
We are told that all men sin, and nothing in Scripture, absolutely nothing, exempts Mary from the rest of the human race. She needed as savior as much as you and I.
The latter part of your statement, "or to subsequent sexual activity," points to the reason so many RCs have so much guilt and anger and confusion over God's gift of a healthy, marriage-sanctified sexuality.