Do you have absolute proof that she did not?
When the dogma of raising MAry to a status which the Bible / the Word of God does not support or identify, the authors of that 'tradition' did not have the knowledge of embryology we have today. It was not conceivable to them that an embryo could be created outside of the woman's body then introduced to her body for gestational support. This is another way of saying they assumed facts not in evidence. ONLY if Jesus has half of His chromosomes from Amry would it be necessary that she be without sin in the conception of Jesus.
The term 'conception' is used in two distinctly different way outside of Embruology. It is sued to ondicate the fusing of chromosomal complement from the father and the mother (thus called fusion of haploids) to form a zygotic aged human embryo. The other way the term is used is to signify the implantation of a morulla aged human in the uterine lining of the host mother. The zygote age is a single new life cell. The morulla age is of many dozens of cells of the embryo, prior to division into the placenta building cells and the body for life in the air world cells. But we have only the indication, from what the Angel told Mary, that a morulla aged human was to be implanted or conceived in her.
The tradition formers assumed both uses of the term 'conceive' and therefore attributed to MAry details not in evidence. So I ask, how would sin have been passed from mary to Jesus during gestational life?
Forgot to give you the passage: Luke 1:31 Behold thou shalt conceive in thy womb and shalt bring forth a son: and thou shalt call his name Jesus. Douay-Rheims Bible.