Originally, Islay was planning to wear the raiment of a Spanish Christian Princess. Garb notes are captured here. For the Moorish fashions, see here.
The Research of Isabel Ximenez de Gaucin, who specializes in 13th century Spanish Christian costume:
(First row, second column: Leonorís Pellote. Second row, first column: Leonorís Brial. Second row, second column: detail of the lacing on the Brial.)
Spanish ladies' camisas, or chemises, came in two main styles in the 13th century - loose, and tight. And I mean *tight*. The tight camisas could be heavily embroidered on the chest and sleeves, in which case it was called a camisa margomada. Thereís an excellent picture at http://www.jessamynscloset.com/13thcbasic.html None of the camisas survive from the burials at Las Huelgas but linen and cotton are both possibilities. (The funerary clothing of DoŮa Maria, a child princess who died in 1235, includes a camisa and calzas of cotton.)
No miniatures clearly show the cut of the camisa, so any generic medieval chemise pattern will do. For the tight-fitting camisa, add side lacing, and tailor as necessary to make it fairly snug fitting in the torso. (The forerunner of the Gothic fitted dress? Enquiring minds want to know!) Were both sides laced, or just one? None of the miniatures show both sides at one time, so we can't be sure!
The main dress for Spanish ladies, the brial came in two varieties. The style which was worn over the camisa margomada had no sleeves, and only had the narrowest bit of fabric over the chest to flaunt the embroidery on the camisa underneath. It was also snug, and laced up one side. For a line drawing of an extant brial, go here - the second row, first column: Leonorís Brial. Second row, second column: detail of the lacing on the Brial. (Leonor died in 1244.)
According to Isabel, who has researched and recreated this style, the lacing on the brial does not appear to have been "load bearing" - any constricting or shaping would have been done by the camisa layer. Oh, and yes, this does mean that the brial side lacing is directly over the camisa side lacing, and their is some chance of skin showing.
Debate rages as to whether Leonor's brial and pellote were created and worn exclusively for her funeral. The garments each measure nearly six feet in length, which would make her at least seven feet tall if the hems just touched the floor. If the garments were rather intended to pool on the floor when standing or sitting, they would have posed quite the challenge for walking since not one but two layers would need to be hoisted out of foot's way.
Some brials had sleeves, though the snug fit (achieved through side lacing) appears to be a common feature.
Sideless surcote, again to show the decorative layers underneath. In addition to conspicuous consumption, the pellote also served as a functional layer of warmth when lined with fur. Rabbit fur provided a cost effective option when the fur wasn't readily visible.
The Wild and Crazy Spanish Hats:
Her Highness would of course wear Her Coronet, and Spanish royal ladies are usually seen with a sheer veil draped over their crowns, their hair curling around their shoulders.
The wealthy aristocrats' daughters who served as ladies-in-waiting, however, sported some of the most outrageous hats seen in Europe at this time. The hat, called a toca, may be "cake" or "saddle" shaped, and came in a range of heights. Leonor was buried with a toca, which shows the ruffles were formed from two pleated edges of a strip of silk which was folded in half and stitched to a vellum base. Additional strips of silk pass under the chin or behind the head to secure the toca; some ladies even sported a band, called an oral, which passed over the nose and obscured the mouth. This last fashion may have been inspired by veiling practices among Moorish women. (See Anderson.)
(Wimples, barbettes, and hair nets are all common among the up-dos of the middle and lower classes.)