I think most of the time she's calm under pressure, specifically the raid on the Governor's Mansion in COTBP. She had a plan for her maid and thought very quick and on her feet. Maybe calm's the wrong word. But she doesn't fold under pressure. She usually has an idea of what to do about it.
She's pretty calm with that gun pointed at Beckett. He's not going to talk her into putting it down, and most girls would probably be a little too intimidated by Jack, but we've seen she can handle him. She makes wrong decisions sometimes, but I have to say, I would rather have a plan and be wrong then just fall on the ground and beg for mercy and wait to be rescued.