Morgana is following, looking for a way out as well, but the knock stops her in her tracks.

On the third knock, Morgana's identified the door. She pauses, and is about to call out a command to show one's self but the pause in running means that she's hearing something else, far more frightening, to her.

There's another click from the turret.

So, she makes the decision. "Whoever that is will have to deal with us, before you get hurt again."

She's clearly not as concerned about herself as he is.