Board Thread:Questions and Answers/@comment-30303676-20161023153004/@comment-1429792-20161023164258

Because she disobeyed him, they are supposed to only kill people they are contracted to kill. They cannot just kill whoever they like, which is what Arya did. It has nothing to do with justice or deserving it as I understand it. Also I believe the tv series consolidated Jaqen and another Faceless Man in to one character. In the book these are two different people.