There is a reason the Constitution vests “the executive power” in a single person, the president. To read it otherwise is to invite the kind of chaos in executing the nation’s laws that the founders were determined to avoid. Ms. Yates’ correct path was to resign, if she felt as strongly as she did about the ban. However, she didn’t.
She was canned because she refused to have the Justice Department defend the White House’s executive order temporarily putting a hold on entry into the US for citizens and refugees from seven Muslim-dominant countries. which was her job to do..
Although Ms. Yates stated she had qualms about the legality of the order, she did not in fact argue that the EO was illegal and admitted that the Justice Department’s Office of Legal Counsel had agreed that the order was “lawful on its face and properly drafted.” Far more important to her, as is clear from her own statement, was whether the executive order was “wise or just” and her view that the department must not only divine what is legal but “always seek justice and stand for what is right.” Since Ms. Yates judged the order to be neither wise nor just, she chose to have the department not defend the EO as it was being challenged in various courts.
Of course, that is not the Justice Department’s job, nor is it the attorney general’s responsibility to stand in the way of an executive action that has been judged legal, even if flawed policy.