39. Certainly, in the full and strict meaning of the term, only Jesus Christ, the God-Man, is King; but Mary, too, as Mother of the divine Christ, as His associate in the redemption, in his struggle with His enemies and His final victory over them, has a share, though in a limited and analogous way, in His royal dignity. For from her union with Christ she attains a radiant eminence transcending that of any other creature; from her union with Christ she receives the royal right to dispose of the treasures of the Divine Redeemer’s Kingdom; from her union with Christ finally is derived the inexhaustible efficacy of her maternal intercession before the Son and His Father.
40. Hence it cannot be doubted that Mary most Holy is far above all other creatures in dignity, and after her Son possesses primacy over all. –Pope Pius XII from Ad Caeli Reginam (On Proclaiming The Queenship Of Mary)
This document, in its entirety, should be required reading for the day. It traces the history of devotion to Mary from the earliest days, through quotations from existant writings and works of art of the faithful, demonstrating the logical corollaries of the Kingship of Christ through the implications for His Mother, Mary. As a document, it is fairly short, but packed with illuminating themes.