Having known people like that I can sorta see Hillary's stance, though not approve of it. She kept repeating the mantra that the emails in question were not marked "Classified." Hillary's position was that they weren't marked correctly. Therefore it was State Department's problem, not hers.
We've all known or maybe worked with people like that. If someone else made a mistake, that was that other person's problem. She was not going out of her way to point it out or modify her behavior based on what that other person should have done.
She wanted to show her intellectual superiority so much she simply took what the State Department sent to her and applied her own standard. If they didn't mark it in the correct manner -- tough luck. Not my problem. Stupid State Department.
Of course, what makes the State Department stupid is that they went along with it. There was also the fear factor, of course. Employees there were probably scared to death of her.