As requested by @lavender-100, some details about Layla's physical appearance. Some novel spoilers in this post so be warned!
We first meet her in Book 10, where she is a trainee priestess at the Temple of Ashi in the Oxus region. She is initially described as tall, well-proportioned, and wearing women's clothing that is white with blue trim. She is even taller than Farangis (and Farangis herself is described as being taller than average for a woman and a little taller than the average Parsian man). For reference, Layla is about the same height as Narsus.
Layla's hair is short, though no hair colour is mentioned. Her clothing is also short, and her long, slender, tanned arms and legs are exposed to the sun. She has a broad frame and a muscular build, and owing to her strong physique she almost looks like a young boy.
I have some illustrations to share, too!
Book 10, Layla versus Namard, illustrated by Yoshitaka Amano.
Book 11, Layla versus Alfarid, Kermine in the background. Illustration by Shinobu Tanno. You can see the silver bracelet on Layla's left arm clearly here.
Incidentally, the design of these silver bracelets given to the three girls (Parizad, Fitna and Layla) is described as being engraved with a design of a young man on the back of a bull, stabbing the bull in the head with a short sword. I'm assuming Tanaka drew his inspiration for this from tauroctony scenes.
Anyway, as you can see, in Tanno's illustration Layla's hair is white. It's possible I missed a description of her hair colour somewhere in the novels, but it's definitely not mentioned in Books 10 or 11, so I'd say it's possible this is a stylistic choice by Tanno that is intended to show the effects of Zahhak's blood on her (a form of mind-control). Since Don Ricardo's hair turned completely white after his encounter with Zahhak, I can see why Tanno might have chosen to portray Layla with white hair here, but I'll keep an eye out for actual written descriptions of her hair colours later in the novels just in case it's mentioned.
Book 12, illustration by Shinobu Tanno, Tahamenay in the process of throwing herself in front of Gieve's sword in order to protect Layla. Gieve came very close to accidentally killing Tahamenay here but thankfully Isfan's quick reactions saved her life as he deflected Gieve's blade.
Book 13, another Shinobu Tanno illustration. Layla and Ilterish get to see Zahhak for the first time. The mage is Gazdaham.
The outfit Layla wears in Book 13 is described as completely unadorned, and she's dressed like a man, with only the silver bracelet appearing out of place with her warrior's attire. Even so, it's mentioned that Jalair thinks she is very beautiful.
(In terms of height, Ilterish is about average height for a man, so Layla's actually a bit taller than him.)
