I like this actress for Nymeria Sand:
She's a friend of mine & has done some random stuff, though her most prominent role is in a feature which isn't finalized yet.
She's Swedish & travels back & forth between Stockholm/London since she has family there, but I know for a fact she's relocating to London full time.
She has the look (pale skin, dark hair, tall, high cheekbones, full lips, is quite slender) down! Well, apart from the eyes.
Looks good in blonde too & could probably pass for Tyene as well.