Jesus paid the temple tax even though He was not obliged to
He did this so that others could would not be scandalized against Him
I see Mary having a sin offering as the same thing
also, God is the savior of Mary
He saved her by keeping her from sin
just like if someone pushes you out of the way of a bullet that person "saves your life" even though you did not die
saving can be either restorative, or preventative
Occam's razor, oft cited by fictional Sherlock Holmes, is correct nonetheless: "the simplest explanation is most likely correct." This follows because the hypothesis with the fewest assumptions has fewer places where error can hide.
Sherlock Holmes would discount your hypothesis, it assumes "Mary knew she was sinless." Nothing in the context indicates she did. The simplest explanation for Mary's sin offering, is she had sin preventing atonement, at-one-ment with God.
Moreover, your theory presents an insurmountable dilemma, if we judge what sinless people do by the revelation of Jesus' impeccable character. Sinless folk do not deceive others. If Mary knew she was sinless, then she deceived the priest into offering a bloody sacrifice for sin that doesn't exist, a sacrifice the Law of Moses didn't command, and in effect made him a sinner.
Its antithetical a "sinless" person deceive others, and cause them to sin, and that a priest of the Most High God.
Another dissimilarity between Christ paying the temple tax, and Mary's sacrifice for sin, by custom Christ owed the Temple Tax (Neh 10:32 cp Ex 30:13-15), but it was the Law of Moses Mary owed the sacrifice for sin.
While Christ chose to pay what was required by custom, to further the Kingdom and not "stumble", Mary's action had no effect on those seeking God. It all was a private matter, no one would be stumbled from obeying God, they would only be angry at her. Whereas Christ's motive is "selfless," your hypothesis makes Mary guilty of "selfish" motives. Judging by the sinless person of Christ, that is hardly the character one expects to see in a "sinless person."
So your first argument should be impossible for you to make, given your high regard for Mary.
Relevant to your argument is other scripture indicating Mary was not sinless:
34 Then Mary said to the angel, "How can this be, since I do not know a man?"
35 And the angel answered and said to her, "The Holy Spirit will come upon you, and the power of the Highest will overshadow you; therefore, also, that Holy One who is to be born will be called the Son of God. (Luk 1:34-35 NKJ)
If Mary were sinless, then there was no need for the power of the Highest to overshadow her, so what was born would be "Holy", that is, separate from the sinfulness of man.
As for your second argument, it begs the question why Paul never cited Mary as the exception to the rule. If she were immaculately conceived like Adam and Eve, then she was not under the penalty of death for sin:
Gen 2:17 "but of the tree of the knowledge of good and evil you shall not eat, for in the day that you eat of it you shall surely die."
1Co 15:22 For as in Adam all die, even so in Christ all shall be made alive.
Rom 6:23 For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.
Wouldn't the apostle John list Mary as the exception to this rule?
1Jo 1:8 If we say that we have no sin, we deceive ourselves, and the truth is not in us.
Your second argument also violates
parsimony, occam's razor. Because it adds the unique and hitherto unknown entity of a person born sinless before Christ, who died for everyone's sins.
Before Christ, before His instructing the masses, you have the entity of a fully knowledgeable Mary knowing God saved her, before time. Unlike everyone else around her and in history, God is her saviour differently, pre-conception.
Nothing in the scripture indicates Mary believed in pre-existence of souls, let alone being saved even before she was conceived. And there certainly isn't anything in her declaration God is her savior, that the saving act was something that happened in the past, before she was conceived. Parsimonously, its just like the statement any sinner makes of a God who continually saves from sin, expressing the confidence He who began saving, will do so even unto death.
To sum up, your arguments contradict scripture, and have consequences someone with your high regard for Mary, must surely reject.
If what you argue is true, then Mary is a deceiver involving a priest of God into offering "strange fire" to the Most High God. It is "strange fire" because the law of Moses never commands blood be shed in sacrifice for sinlessness.
No doubt it was God's merciful grace that kept the fire from going forth, to consume the priest:
1 And Nadab and Abihu, the sons of Aaron, took either of them his censer, and put fire therein, and put incense thereon, and offered strange fire before the LORD, which he commanded them not.
2 And there went out fire from the LORD, and devoured them, and they died before the LORD. (Lev 10:1-2 KJV)