Another facet of the Unicorn symbol to chew on. The depictions mentioned earlier invariably involve a unicorn being imprisoned in some way. The black unicorn was frozen in place for a magical cardiectomy, the unicorn in the tapestry was corralled and Maleficent kept the creature as a pet. All symbols of submission, imprisonment etc. all very relevant to Regina’s position as a prisoner of the Darkness. Quite often in heraldic depictions of unicorns they are bound/chained to indicate that they’ve been broken like a common pony other times with their bonds cut to indicate their freedom.
Likewise the restless unicorn it is said can only be brought to bay by innocents (generally-speaking virgins, quite often female). Like a unicorn Regina has a restless nature that only Henry has been able to calm. While attempts made by anyone else have all ended with them getting burned. Henry’s childhood innocence has calmed Regina’s spirit and his believing heart give her hope. Woe betide the rest of the family if that changes.
Custodian of Graham's darts, Rumple's spindle and Robin's quiver