Who is Arya Stark from A Storm of Swords and what is their importance?

Aryan from A Storm of Swords is the youngest daughter of Ned and Catelyn Stark. She is a tom-boy and likes to learn sword play. In this novel, she's been with Yoren, whose plan was to drop her off at Winterfell on his way to the Wall in the North. When he is killed, Arya and her companions take off on foot. They are captured several times, with the last time threatening to end their lives.

Later, when Arya escapes from Beric, she is captured by Sandor Clegane who aims to ransom her back to her mother at the Twins (where the red wedding is taking place). When they get there her mother has already been attacked. Later, Sandor is wounded and she is able to get aboard a ship using Jaquen's coin.