In a moment of need, Aang summoned for the past life of the former Airbending Avatar, Yangchen. A woman who Aang thought would not only confirm what he needed to do, or not do in this case, but also guide him on what to do.
However, though Yangchen was from the Air Nomads, she revealed how the Avatar cannot be a true pacifist like Aang desire. That sometimes action needed to be taken, and that as the Avatar, he must blend his personality with the personalities of the other nations to become something greater.
In the comics, Yangchen reappeared and helped guide Aang through an intense confrontation with an angry spirit. It was also her that allowed him to reconnect with his Avatar line after he intentionally cut it.