Upvote:4
A Catholic source gives the following information about Mary under the heading "Mariology":
"Thus she became, as Pius XII said (Constitution Ad caeli reginam, 11 October 1954: DS 3913-17), "Queen of Heaven". This title, which comes from mythology but is used in a non-mythological sense, indicates the lofty position of Mary in the divine economy and in the historical course of salvation." Encyclopedia of Theology, article by Michael Schmaus, page 898, Burns & Oates, 1981.
This quote does not give any date, either specific or even for any one particular century, when Mary was spoken of as being "Queen of Heaven" in Catholic theological circles, and in an 8-page article not another word is said about this title. The quote only tells us that "she did become" so entitled, without saying when or how. The preceding section leading up to mention of what Pius XII said in 1954 has not a clue about this title; it speaks of her many other titles in depth. But it does say that "Patristic testimony begins only in the 6th century", which falls within the 800 A.D. time-limit suggested in the question. However, it remains to be seen whether any of the Church Fathers up till then can be quoted as using that title. Given their awareness of Old Testament scripture, they would know that in Jeremiah 7:18 & 44:17-23 Ishtar was the Babylonian version of the Queen of Heaven.
The reference to mythology cannot be ignored, however, for it invites comparison with the mythological goddess who was known as Queen of Heaven - the Egyptian Isis. She was entitled Our Lady, Queen of Heaven, and Immaculate Virgin. According to Chaldean beliefs, Semiramis (the wife of Nimus or Nimrod), was exalted to divinity with the title "Queen of Heaven". As the Christian church gradually took over temples of Isis and the image of the Earth Mother, complete with the Mother and Child statues, it appeared as if those became incorporated into the Catholic religious system β but not by all Christians. Many early-century groups refused to go there.
However, the title "Queen of Heaven" certainly did begin to apply to Mary in Catholic thinking. When, exactly, may be as difficult to nail down as trying to fix jelly to a wall.