I don’t know, but there’s a possibility that her hand over her heart is the artist’s understanding of the Scripture from Luke, when Simeon prophecies that “a sword shall pierce your heart”. Did Simeon know that when the sword piercd the heart of Jesus that, in spirit, Mary’s heart would feel the piercing?
I had a friend whose son was murdered in the process of a theft. This grieving mother told me that she understood why we are told that a sword peierced the heart of Mary.
What mother can endure watching her Son being crucified, and not have a piercing of her heart.
Sorry—I posted 2 versions—without realizing it.
Good points.