Despite her faith being more of a result of the conditioning she has recieved then true belief, Ash's thanks to the Emperor is genuine. She prepares her blade to finish the fallen marine, but as she notices Rosette moving towards him, she aims her neural shredder at her. She's ready to shoot her teammate for her apparent betrayal, but stops when she notices that Rosette is neither attacking her nor helping the injured marine. Ash lets her to execute him, but doesn't lower her weapon, it may still be some sort of deception and the sister may turn against her when Ash lowers her guard. She doesn't know if the weapon have enough power for another shot, but then, neither does Rosette.
"I wasn't aware women from your order are allowed behave like that." Ash is watching Rosette closely, but her gaze have a tendency to wander from the weapon in her hand to other parts of her naked body.