There may be some difference in the RC construct, but in addition, when God wants us to know that someone or something is pure and without sin than He tells us in a way that is not problematically derived.
“Which of you convinceth me of sin? And if I say the truth, why do ye not believe me? “ (John 8:46)
“Who did no sin, neither was guile found in his mouth: “ (1 Peter 2:22)
“For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him. “ (2 Corinthians 5:21)
“For such an high priest became us, who is holy, harmless, undefiled, separate from sinners, and made higher than the heavens; “ (Hebrews 7:26)
“The law of the LORD is perfect, converting the soul: the testimony of the LORD is sure, making wise the simple. {8} The statutes of the LORD are right, rejoicing the heart: the commandment of the LORD is pure, enlightening the eyes. {9} The fear of the LORD is clean, enduring for ever: the judgments of the LORD are true and righteous altogether. “ (Psalms 19:7-9)
The question is, if God could God bring forth His pure word thru men who were sinners, though overall holy, (2Pet. 1:20-21) then almighty God could do the same as regards Mary. And such esp. ought to be allowed if transubstantiation is believed, even so far as that the blood of Jesus was in the stomachs of the (kosher) apostles while Jesus was sitting or reclining next to them.