https://www.cnet.com/news/game-of-thrones-one-battle-of-winterfell-detail-you-probably-missed/

Where did she come from? How did she sneak past the White Walkers? To some it seems a bit Arya-ex-machina, with the young Stark's Hail Mary leap of faith coming out of nowhere and not really making sense. However, there's a small detail from the episode that adds an essential piece to the puzzle.

Before Arya lunges at the Night King, we see Jon Snow trying to make his way into the godswood, where Bran Stark and the Night King are. The path is blocked by Viserion, the White Walker dragon. Jon tries to run past him, but he's spotted by the dragon. Jon ends up trapped behind the battered remnants of a wall and decides, with nowhere left to run, to confront Viserion. Except he doesn't raise his sword, he just stands up and yells.