Maisie Williams was spotted on the Game of Thrones Season 7 set in a costume reminiscent of the Northern region/characters. Her costume is pretty similar to Jon Snow's Stark costume in Season 6.
these photos have been released from the same set in which Kit Harington was photographed with Jeremy Podeswa who is directing episodes 1 and 2.
Meaning Arya makes it back to winterfell as early as the first or second episode of Season 7.
[Spoiler (click to open)]well this officially kills all the arya valonqar theories lol and the arya will steal jaime's face to kill cersei theory. for whatever reason, it seems like arya decides to let go of her need for revenge against cersei.