Polar Battle Dress

The sleeveless overdress is made of a dark fine chain mail, at least one fitted piece for the bodice, linked just past the hip to a wide skirt.
Underneath is a heavy grayish brown dress, worn with dark boots.
About the neck and shoulders is a piece of fur, golden and long-haired. It's been suggested that this is fur, shaven from Aslan's mane, a striking statement of defiance: a tactic to instill fear and grief in the opposing army!
It's probably a separate wrap, since the bodice is chain mail. The action figure suggests armholes, therefore, a wearable separate piece.
In place of her melted crown, Jadis wears a golden plate helmet or headdress. Although the colors are somewhat skewed in the large promotional painting, above, it's distinctly gold in other images. Angular and spikey, the shape is like a stylized animal skull. It extends underneath about three-quarters of her hair, probably attaching to itself.
Otherwise her hair is worn free - thawed out of the dreads - and it streams out from underneath. The color seems a bit different: a lighter straw-color.
She also holds a spear in her hand, which has appeared several times in different pictures and concept art. Whether this is her wand or not, we don't know.