"In regards to the placement of Mary, she is typically on the left in light of the fact that placed there, she is on Jesus’ right hand from “his point of view” — from the point of view of someone looking out from the sanctuary.This is in accordance with the Jewish tradition of having the Queen Mother sit at the right hand of the King. It is narrated in 1 Kings, “Bathshe′ba went to King Solomon, to speak to him on behalf of Adoni′jah. And the king rose to meet her, and bowed down to her; then he sat on his throne, and had a seat brought for the king’s mother; and she sat on his right” (1 Kings 2:19).
Pope Pius X confirms this tradition in Ad Diem Illum Laetissimum by declaring “Mary sitteth at the right hand of her Son.”
Another explanation is due to the fact that the left side of the church was known as the “Gospel Side” of the church and Mary is seen biblically as the “New Eve,” with
1- Mary plays NO ROLE in Salvation
2- Mary isn't sitting on either side-she is dead awaiting the resurrection in her grave
3- Where in Scripture is the "left side" called the "Gospel side"?