One of the perspectives I really like about GoT is that it does not allow characters to forget who they are, or once were. Within us, there are innate drives, coping mechanisms, behaviors, that have been fostered during out core formative years. We may be 20, 50, 80, but in a way we still have connections to that inner being, and it sometimes shows in how we act, especially within a certain context.
When is the last time we saw Arya, playing/training with weapons in the Courtyard, her sister and others watching... it's her chance to be the precocious 8 year old kid out dueling her brother, shocking people as to her skills and ability, simultaneously upending the family order of her being the youngest, always the child, and the expectations of who and what she should be, as a result.
I found that scene as Arya as anything we've seen. It is who and what she is, at heart... from the very first scenes of the film. A direct connection with the introductory, foundation-building episodes before we knew where any of this would go. All we knew was that this Ned guy had to be in for a good long run in his character on this new TV show with a huge budget, cool fight scenes and plenty of male-friendly soap operatic dialogue and ennui (ok, I just wanted to say ennui, but it's as good as anything I suppose).