The Gospel of Luke (c. 60 A.D.), (Luke 1:28) calls Mary “Kecharitomenae” (“Full of grace” or “perfectly graced”). Thus, when we first meet Mary in Scripture, even before she assents to become the mother of the Messiah, she is already Baptized into Christ and free of all sin.
Also the idea of Christmas being Jesus’ birthday seems like a stretch as well.
The date of Christ's birth is not dogma. The history behind how that date was arrived at, goes back to ancient times.
Let's not forget that Mary was the first Christian and the first Evangelist because her first act after she assented to the Holy Spirit was to go and proclaim Him to Elizabeth.
I take my lead on Marian devotion from JPII who said that we are to ask Her help in forming the Christ within us as God asked her help to form the Christ within her. He spent 30 years with Her, three years in His ministry with the Apostles, three days in the tomb and three hours on the cross. I would say She did a pretty good job on Him and He on Her.
Peace be with you