In one of the biggest moments in Game of Thrones history, Arya killed the Night King and saved the world from the wights and the White Walkers. In Game of Thrones season 8, episode 3, "The Long Night", Arya slaughtered several wights before later being trapped in the corridors of Winterfell. It was then Beric and the Hound who saved Arya from the Army of the Dead, only for her to fulfill her purpose in The Great War by killing the Night King himself.
After being saved by Beric, who was resurrected several times over the past few years because the Lord of Light believed he had a purpose to accomplish, and the Hound, whose purpose throughout Game of Thrones' eight seasons has partly been to safeguard Arya, she saw Melisandre, aka the Red Woman, one more time in the great hall and was retold a prophecy that she first heard in Game of Thrones season 3. She didn't know what it meant then, but she did now... when it truly counted.
In Game of Thrones season 3, Melisandre told Arya: "I see a darkness in you. And in that darkness eyes staring back at me - brown eyes, blue eyes, green eyes. Eyes you'll shut forever. We will meet again." Arya brings up the prophecy one more time during the Battle of Winterfell, but when Melisandre tells her "blue eyes," that's when Arya understands what she must do: kill the Night King and shut the all the blue eyes forever. At least the ones born from the Night King.
Arya's time training to be one of the Faceless men and essentially the Game of Thrones version of an assassin, she was doing more than just avenging her family. She ultimately learned everything she needed to kill the Night King at the exact moment that it needed to happen. This was her destiny, with everyone - from the Hound to Beric to the Red Woman herself - playing a part in getting her to where she needed to go. Perhaps she was Azor Ahai. Or perhaps not.
Regardless of whether or not Arya fulfilled multiple prophecies or just the one Melisandre told her, she came close to dying during the Battle of Winterfell multiple times, but she kept escaping death until she was finally able to kill the Night King. But what's interesting, and perhaps a lingering consequence of her actions, is what happens to her now that the Night King has touched her. She just might be the only person in Game of Thrones' history to be physically touched by the Night King, not including Bran's own mark.
Game of Thrones season 8 continues on Sunday, May 5, on HBO.