Who's the chick on the poster?

By Turin, in Days of Ice and Fire 2013

Looks too old to be Arya.

Appears to be Asha and her turnip from the Queensmoot.

My first instinct was Arya, but she does look a little old. I agree, it may be Asha. Only I thought she had pinecones at the Queensmoot.

“And last, the gold of Winterfell.” From the third chest came yellow turnips, round and hard and big as a man’s head. They landed amidst the pebbles and the pinecones. Asha stabbed one with her dirk. “Harmund Sharp,” she shouted, “your son Harrag died at Winterfell, for this.” She pulled the turnip off her blade and tossed it to him. “You have other sons, I think. If you’d trade their lives for turnips, shout my nuncle’s name!”
.

Ironborn, he knew at a glance; lean and long-legged, with black hair cut short, wind-chafed skin, strong sure hands, a dirk at her belt. - A Clash of Kings