If you watched this week's episode of Game of Thrones, you probably gasped and screamed "NOOOOOO!" when this happened.
But a lot of people have noted that Arya was playing it pretty dumb, standing there in the open after having just betrayed a group of professional assassins.
Ok...so we can all assume that fight scene was an act....but I figured its worth some suggestive ideas. So....
# Before the scene she was seen flaunting Money to the Westeros Captain in order to get the word out there that a young girl was on her way to westeros in the morning.
# Then she chooses an open spot to try and avoid an easy death check after the fight. (Bridge)
# We can assume she knows enough from training to figure the waif will attack to the body. So I believe she has 1 or more pigs blood pouches around her body. She knows where and how to do this because last episode...she saved the actress. The actress then provided her help to make the scene on the bridge large and realistic.
# She then leaves the water and leaves a trail of blood....to lead her enemys to her. Expecting an unarmed (because she choose not to show needle during the fight scene) and injured girl; they will instead walk down a dark alley and be met with an uninjured girl who knows how to fight in the dark and carrying a sword.
Need more proof? How about this: Arya saw that very same face back in Season 5.
If that doesn't help put you at ease that Arya is in control, try out this crazy theory from redditor catNamedStupidity that Arya and the waif are the SAME PERSON.
So here are a few things which are interesting about the waif.
# She is only seen by either Jaqen H'ghar or by Arya.
# She has a very incredible back story, much like Mercy or Cat of the Canals.
# She know's what Arya is doing, all the time. She knows when she lies. She can tell where she is.
# She tries to force Arya to leave. She makes her insecure.
So here's my theory, get some tinfoil..
The waif is Arya. Arya is suffering from some sort of bi-polar dissociative identity disorder. A case can be made that when Arya came to the House of Black and White, the water that she drank induced this in her. In a way, The Waif is no one. Her only mission is to kill off Arya, the inner Arya, the one who can never be one of them.
This is why Jaqen H'ghar always wants the Waif to leave the room before he begins talking to Arya. He essentially wants Arya to stop behaving in a dual personality manner. He just wants to talk to Arya. So the Waif leaves. Just when Arya is alone, she appears again.
When the waif asks Jaqen H'ghar, "You PROMISED", it's actually Arya. Arya has finally asked to kill her inner self. Al lot of people have observed that Jaqen H'ghar looks a bit pleased with himself when he permits the Waif.