That particular image is often called “Seat of Wisdom” (aka “Sedes Sapientiae”). Basically, Mary is serving as a throne for the child Jesus. Jesus is the Word; he contains the Divine Wisdom within him. Mary is the human fulfillment of “Wisdom” as in Proverbs, ie, the ideal wife and mother, etc. Usually there are elements of kingship and dominion in the composition, but their distribution/arrangement varies a lot. But it’s always important to remember that all of Mary’s power and prestige comes from her role as the Mother of God (the Mother of the King), and that it is used to direct people to God. She is never drawing attention to herself; in these compositions, she’s presenting us to her Son, and her Son to us.
Here, you see an uncrowned Jesus holding an orb-- a symbol of dominion-- while sitting in Mary’s lap.
Here is an image from a 12th c. Bavarian Romanesque church, where Mary is the one holding the orb, with Jesus in her lap, and neither is crowned.
A late 12th c. statue where Jesus has the orb, and Mary the crown, and both are seated on the throne.
Here, Mary has a crown and scepter, and is seated on a throne, but the child Jesus stands on her lap and blesses everyone.
This one has Mary and Jesus both crowned; Mary holds the scepter, and Jesus holds the orb. (The filename claims it’s 9th c., but it’s really 19th c.)
Here’s one where Jesus holds the orb, and is crowned, and sits in the lap of a crowned Mary.
This graphic explains some symbolism in an Our Lady of Walsingham statue, which has a good deal of overlap with a Sedes Sapientiae-type arrangement.