From the show's perspective Ayra admits that she did remove The Hound from her list. She was confused about her feeling towards Sandor Clegane after the adventures. While we may not know the exact moment this happened, the whole story lines allows Ayra to realize that not all people can be defined as simply "good or evil".
Jaqen knew Arya was lying when she said she hated The Hound.
(Starting at about 0:12, emphasis mine)
Ayra: A man called The Hound, Sandor Clegane. He was trying to sell me, but was wounded in a fight. He begged me to kill him, but I wouldn't. I left him in the mountains to die. I wanted him to suffer, I hated him - - -
Jaqen hits Ayra with the stick to indicate she is lying
Ayra: (with stronger inflection) I hated him!
Ayra: (raising her voice) That's not a lie!
Jaqen: A Girl lies. To me, to the Many-Faced God, to herself. Does she truly want to be No-One?
Ayra later admits she took him off her list.
(Starting at 1:09 in the linked video, emphasis mine.)
Waif: Tell me about The Hound.
Ayra: Also dead. Ayra Stark left him to die. He was on her list.
Waif whacks Ayra with the stick to indicate she is lying
Ayra: He was not on her list anymore. She'd taken him off it.
Waif: Why? Didn't she want him dead any longer?
Ayra: She did and she did not.
Waif: She sounds confused.
Ayra: Yes, she was.