Mary is the Queen of Universe because Christ is the King of Universe.
To understand her Queenship, one must understand how who the Queen of the Davidic Kingdom in the Old Testament Jewish monarchy was. It was the Queen Mother. The Kings had many wives, none of whom could be called Queen. That honor was reserved for the mother of the King. We see this in the role Bathsheba played with respect to King Solomon and the occasions when the Queen Mother acted as regent on behalf of juvenile successors to the throne.
When Bathsheba went to King Solomon to speak to him for Adonijah, the king stood up to meet her, bowed down to her and sat down on his throne. He had a throne brought for the king's mother, and she sat down at his right hand. - 1 Kings 2:19
Hence by Jewish tradition, the Jews expected the Mother of their King to be the titular Queen. The same holds true for the New Kingdom of God. If Jesus is King of this new Kingdom, then Mary should by tradition be his queen.
In Revelation 12, the Women who brought forth a child, who was to rule all nations with a rod of iron: and her child was caught up unto God, and to his throne was seen crowned with of twelve stars. This women is traditionally identified as Mary. And this image of Crown is held to be one of the evidence for her queenship.