Today's feast was brought in by Pius XII in 1954. The fact that Jesus is from the royal house of David must mean that Mary is the mother of the new king of Israel and thus she is Queen.
1954 was also the year when Pius XII declared the Assumption to be a dogma. In order to bear Jesus, Mary was given the grace of being free from sin and thus when her life on earth ended, tradition holds that she was assumed into heaven. There is no written record of this event, tradition (word of mouth) was handed down from generation to generation of the event. As time passed, the Church pondered seriously on this event and listened to the theories presented by contemporaries. Some saying that Mary was nothing special at all, just a carrier of Jesus. Did her body face corruption like the rest of us or not?
We have to remember that death came into the world because of sin. Prior to the fall of Adam and Eve, there was no death, no sin. Taking all this into consideration, Pius XII declared the dogma of the Assumption of Mary. Remember, that dogmas are declared beliefs by the Church to be true, infallible and must be believed by all believers. No cafeteria style beliefs accepted in the Catholic Church!
Feast of The Queenship of The Blessed Virgin Mary Stephen B Whatley, 2008
Today's feast starts off at the "end" of the Assumption.
Again, Church Father's reviewed the writings of old and new testaments and followed this line of reason; Jesus is king of heaven and therefor Mary, as mother of the king, must be Queen.
Pius XII brought out this connection between the Assumption and Queenship by placing today's feast just one week after the Assumption.
Even though the Queen of Heaven feast is not a dogma, it is held by tradition to be an event that happened. Note that the fifth glorious mystery of the Rosary, the Coronation of Mary as Queen of heaven, shows that this Queenship of Mary has been understood as of old.