I cannot attest to the Marian interpretation, as I have not consulted a study Bible or commentary about the book of Revelation.
Without further elaboration, I would think that, in the sanctuary of God, the ark is the mercy seat of God, where in the transcendent view of things, God is thought to dwell. There was nothing holier on earth than the ark. It was a visual representation of the presence of God.
Surely, there is one place where God stands alone, distanced even from Mary, and that would be in his sanctuary. I don’t view Mary as being inseparable from God.
(I don’t think what any person thinks about Mary alters her status with respect to the Almighty. Her status is, first and foremost, based on the judgment of God, to which I can neither add nor detract – even if I had a mind to try it.) Mary’s glory is, at best, the reflected glory of God himself.