Although stylized, the image of the Virgin Mary in the Book of Kells is surprisingly detailed, and could serve as the basis for a nice reconstruction. Finnican Dub has a great primer on Irish evidence for early clothing which helps put some of the garments into context. And Christian de Holacombe has an article on the use of metallic spangles on garb, documented to England as early as the mid-12th century. So it might not actually be unreasonable that those three-dot patterns on Mary's mantel were actual real-life decorations, as opposed to a flourish of the illuminator.
I need to finish (start) the garb projects I already have fabric for, but maybe one day...
The headpiece seems to be a yellow/golden veil with the bit around the face trimmed with something. A band across the top, turning to scallops lower down. I thought the scallops were hair at first, but if so, the lavender/pink hood/lining? is under her hair. There's an additional golden band across the forehead, marked with dots - maybe a fillet. Dub reads the pink layer as a hood coming off the leine (tunic) layer, and since it merges with the layer on her chest, that seems right. The yellow veil's draping is drawn very clearly.
A white undertunic is visible high on the neck. The top line (dividing the tunic from her flesh) is black; two additional lines are red. Are these decorations or wrinkles?
Between the white undertunic and the lavender/pink leine is a bit of knotwork, gold on a black background. It's got a border around it, indicating that it's a completed piece. Could be a decorative flourish (this is the Book of Kells, after all) or a legitimate piece of embroidery on the leine. Some kind of metallic possament is possible, but I'm not aware of any evidence for metalwork decoration of that type in the isles. Maybe jewelry - a necklet in the Byzantine style, only... well, those were usually collections of round things, not a solid bar. A brooch?
What's weird is the pleating going on right underneath it. There are a lot of thin folds of the leine gathering around the neck, mostly running vertically - except right under the knotwork, there are a pair of folds running horizontally. Is that some sort of tie at a keyhold neck, gathering all this fabric into pleats? If so, the knotwork can't be sewn in place on the lavender/pink fabric.
There's an odd random line on the left side of the Virgin's face, right at eye level. Is her neck actually white and not peach-colored? That might be a wimple. Then the little white oval is... a lock of hair? A coif?
The lavender/pink garment visible at the neck seems to be the same one forming her skirt. If the outline of her legs is indicative, it's very fine. (Then again, her breasts are explicitly drawn under her brat, and that ought to be a heavier garment. But then-then again, that might be the monks making sure we understand that we're looking at a woman.) The hem is edged with a golden band.
Her arm, though, is in a darker blue sleeve. Dub interprets this as a sort of jacket, which is certainly agreeable to me. I loves me my caftans. Two bands, dark and light gold (or orange and yellow), edge the sleeve. There's a final dark colored band - I think I'd interpret that as decorative appliques set back from the actual sleeve hem. But the final dark band does seem to be closer to the body than the rest of the sleeve. Could be the gold/orange bands have some sort of wrist clasp to narrow the sleeve? Or it's yet another layer, but that seems excessive. We've already got the white undertunic, the lavender/pink leine, and the dark blue caftan.
Finally, the wine-colored brat, edged with a gold band and decorated with small silver spangles. It's fastened with a triangular kite brooch. (Like this one, I think, which is the news article that got me started down this path in the first place!) Interesting notch detail in the brat hem.
Unsurprisingly, this whole 'look' isn't far from the Anglo-Saxon stuff I've been working on. Different in the details, naturally, but the undertunic/tunic/jacket/cloak look, topped with a draped rectangular veil, is very familiar at this point.