I have occasionally noticed that late Medieval representations of our most blessed Lady often show her bare-headed and with her hair over her shoulders and arms. I think of the Marian banner in St John's College (reproduced in Duffy Fires); of the statue of the Assumption in the church at Sandford upon Thames.
And the Roman Pontifical, describing a Queen approaching her Coronation, says that she comes crine soluto. The records of the Coronations of Good Queen Mary and of Bloody Bess agree: she wears her hair loose and 'decently let down on her shoulders'.
I know what you're going to say to me: "Don't be silly ... they were going to be needing to balance a crown upon their heads, so of course hats and fancy hair-does were excluded ... do try to be practical ..."
I suppose you're right ... if, perhaps, a trifle prosaic.
But I still can't help wondering whether there might be some association of a bare female head with regality.
Matthew Sarbiewski, a Pole and one of the associates of Urban VIII in the importation of Horatian poetics into the Christian Latin of the 1620s, describes the head of the Mother of God:
Tu [his friend Rosa] rerum dominam canes,
Et sparsam Zephyrorum arbitrio comam
Nudis ludere bracchiis,
Et nimbos volucrum fundere crinium ...