NO one gives a SIN offering if they haven't SINNED!
Do YOU go to confession just to be chummy with the priest?
So, you are saying that Mary (actually, her parents), should have BROKEN THE LAW.
THAT WOULD HAVE BEEN A SIN.
There is no parallel between the sin offering and modern confession. The sin offering was a prescribed ritual, not a personal confession of particular sins. Confession is NOT mandated on any kind of schedule—i.e., after childbirth, or before marriage, etc. It has everything to do with particular, personal sins of which a Catholic is aware.
Pretending that a passage about a MANDATED RITUAL, a law that applied to every Jew, provides information about the state of the state of Mary’s SOUL, is a classic example of Scripture-twisting.