Mary has two significant appearances in the Book of Revelation.
Most devout Catholics are familiar with one of them:
A great sign appeared in the sky, a woman clothed with the sun, with the moon under her feet, and on her head a crown of twelve stars (Revelation 12:1).
But there is a second, implicit one, immediately preceding the above:
Then God’s temple in heaven was opened, and the ark of his covenant could be seen in the temple. There were flashes of lightning, rumblings, and peals of thunder, an earthquake, and a violent hailstorm (Revelation 11:19).
We know that the heavenly ark envisioned is Mary because she is identified with the ark in the Gospel of Luke. During the Visitation, many of the phrases her cousin Elizabeth says in greeting her are taken from Old Testament accounts of the liturgical worship of the ark of the covenant (see my previous article here for an exhaustive breakdown of the parallels).