Disagree. It's just bad writing. The Waif has consistently displayed contempt and disdain for Arya, but not hatred. She has no reason to hate Arya. As Kiwi has pointed out, it's a jarring inconsistency that the Waif would make such a basic mistake. Equally, as BDF has already detailed, Arya was doing EVERYTHING wrong in terms of how to behave when on the run from an order of assassins who can change their facial appearance - more bad writing. It's a false peril situation in that they want us to fear for Arya, but we all know Arya won't die because the show writers have decided she's a key character.
Having said all that, it was a GREAT episode. The acting from some of the more minor characters was excellent - Lady Mormont, Lord Glover and the Blackfish all stood out for me. I also found myself thinking "I wonder if Ian McShane's character will be revealed to be Howland Reed?"
Unfortunately some of the plot is far too easily signposted: Brienne is going to rock up at Riverrun in time to save the Blackfish from Jamie, and Jamie from himself; The knights of the Vale will appear at the battle of Winterfell, just after Wun-wun and Tormund are killed and when Jon faces certain death, to save the day a la Gandalf at Helm's Deep. The writers would do well, IMHO, to shake up the formula that each season now seems to follow in terms of pacing - we all expect episode 9 to be the "big" episode because it's been that way since forever.
Don't look at the below if you don't want to know about Brienne.
Brienne turning up at Riverrun has already been previewed for the next episode. She is going to try and get the Blackfish to surrender, or she will fight Jaime herself (not sure why).