[MAIN SPOILERS] Where did Arya go?

Arya has wanted to kill Cersei for the longest time. She has already gotten revenge against House Frey for the events of The Red Wedding. She continued to ride south where she was reunited with Hot Pie who informed her that, unbeknownst to her, Jon was now King of the North.

Having not seen any of her siblings in quite some time, she decided to put her desire to kill the queen on hold and proceeded to ride North to Winterfell.

She was surrounded by a pack of wolves and recognized the Alpha as her direwolf, Nymeria. After trying to convince her direwolf to come back home with her, the wolves turn and leave with Arya realizing that Nymeria has changed and is where she belongs, just as Arya herself has changed throughout the series, as noted by her look of determination during the conversation she had with Hot Pie about killing the queen.

After that, we have no idea where Arya went...or do we?

Sansa and Bran have been reunited at Castle Black, with Jon traveling to Dragonstone to meet with Daenarys. Now part of me thinks that had Arya decided to continue riding North she too would've been reunited with Sansa and Bran at some point during the episode. Also, due to the short time for Jon to show up in Dragonstone, one would be led to believe that Arya's journey North would've been just as brief.

It is this reasoning that has lead me to the following:

Arya, after being confronted by Nymeria, decided to change her mind and turn back South to go through with her quest to kill Cersei.

But how?

Cersei had a visitor from the Iron Bank of Braavos who has come to collect on her debt to which Cersei stated would be paid in full in a fortnight, because "Lannister's always pay their debts."

Could it be possible that Tycho Nestoris is actually Arya in disguise?