Here at Christ the
King we traditionally crown Our Lady during May, the Sunday after our
children have made their First Communion. All of the children
come to the Sunday Mass in their Communion outfits and lead the
procession to Crown Mary in this special month. Why do we crown
Mary? The rite of crowing explains: She is the Mother of the Son of God, who is the messianic King. Mary is the Mother of Christ, the Word incarnate. ... "He will be great and will be called the Son of the Most High; and the Lord God will give him the throne of his father David; and he will reign over the house of Jacob for ever; and of his kingdom there will be no end." [Luke 1:32-33] ... Elizabeth greeted the Blessed Virgin, pregnant with Jesus, as "the Mother of my Lord." [Luke 1:41-43]
She is the perfect follower of Christ. The maid of Nazareth consented to God's plan; she journeyed on the pilgrimage of faith; she listened to God's word and kept it in her heart; she remained steadfastly in close union with her Son, all the way to the foot of the cross; she persevered in prayer with the Church. Thus in an eminent way she won the "crown of righteousness," [See 2 Timothy 4:8] the "crown of life," [See James 1:12; Revelation 2:10] the "crown of glory" [See 1 Peter 5:4] that is promised to those who follow Christ.
http://campus.udayton.edu/mary/resources/crowning.html
http://www.fisheaters.com/customseastertide5.html