Meredith clenches her jaw, fighting back any other reaction, though she won't even look at him and doesn't have anything to say (telling him not to touch her sounds too much like a challenge, and she doubts this is a man accustomed to backing down from those. She's past her days of being suicidal, let alone actively so, and these aren't idle threats). Asking just what the mission is seems like something that falls under the category of holding them back — something to ask Sean if she can get him alone for half a minute, then, which she wants desperately. If this is their way out, then all she can do is follow along, nodding quickly.