I don't think it's a sign of her being standoffish. They relaxed formalities in the DQ, and now because they're going home, she's sort of reassuring them, "Yes, this is happening, we'll be home soon, where people give orders in a more formal fashion." I think they might actually appreciate the gesture in that sense. Once they get home, they can get back to the business of having rank and file and structure, which is how it;s supposed to be. Not saying people aren't friends anymore...do you get the gist of what I'm saying?
Suppose you, some co-workers, and your boss are stranded in the deep wilderness after a car accident coming back from a work retreat. You have to band together to survive until somebody comes around. During that time, your boss, by necessity, bonds with you and them, calling you by your first name. You spend two weeks in the wild together, then somebody finds you and rescues you. The danger and fear is over. Things are going back to normal. After medical treatment and counseling, you'll head back to work and take up your old job (not the same person you were before, but still). When you see the helicopter flying in, your boss calls you by your last name again, and you hear it and know that he/she believes this is really happening. You will be rescued now; it's not a dream, wish, or hallucination. It fills you with confidence; if they believe it, so do I now.
