Since there's not much that scares Arya these days, we are convinced she's running from zombie Starks.
I don’t think there are going to be any zombie Starks. I think there is probably some ‘old magic’ in the crypts of Winterfell which prevents the re-animation of Starks as wights.
I think Arya is probably running from a White Walker. I can imagine she is going to be chased into a darkened room where she’ll do a repeat of the encounter with the Waif and kill it in the dark with her dragonglass dagger. This will cause many of the wights who are fighting the allies to drop dead (as in season 7) and will effectively end the battle. Meanwhile, Jon will be somewhere else doing something else to try to kill the Night King.
The women, children and eunuchs will hide in relative safety in the crypts and avoid the battle (D&D have said this is a callback to the battle for Helm’s Deep in the Two Towers) and will emerge after the zombie horde has been driven back. Winterfell will be trashed and they’ll have to retreat south as Chekhov’s Food Stores will have been burnt to a crisp by dragon fire.
I’m probably totally wrong.
My big question is at what point will Melissandre arrive?