Now that Billy was back in their possession, Kitty really didn't see why they couldn't get back to their objective now--Oh but wait. Jack had an crossbow pointed at him. Her first instinct wasn't to shoot, but rather, lunge in front of Jack to his defense, her free hand touching his some haphazard part of his body so that the arrow projecting toward Jack could successfully go through her and him without damage.
"We're not here to harm you!" Which, admittedly, might not have appeared that way, but they really had more important things to accomplish, and anyway she was pretty sure that was Tony Stark.