I’ve seen a lot of people theorizing that Arya’s ending could be that she becomes Lady of Harrenhal. I like that theory, but do you think that Arya would willingly go back to a place where she suffered so much trauma?

Hmmmmmm I haven't really seen a lot of people theorizing this but I do think it has a basis in the books. I don't personally see it as an endgame position for her, although she does have plot connections to Harrenhal. As for her willingly returning there, that could either be a decision she's forced to make or something she chooses to bear for the " greater good". If Arya is in a position where she believes she is able to do some good in that role, I can see her prioritizing that over her own trauma. Either way, I think she will return to Harrenhal/the Riverlands at some point so it will be interesting to see how that plays out.