Toward the end of the movie when Ripley and Newt discover the Queen, the Queen appears to be HUGE. Like 4 times the height of a human. When I first saw this scene, I was awe-struck by the size of her.
Then the Queen breaks away from the "reproductive tube" and starts her chase on Ripley and Newt.
Well in the scene where Ripley and Newt are in the elevator and the Queen confronts them, she doesn't seem so huge anymore. More like the size of the drones. Small enough, in fact, to be able to fit in the elevator.
Then when the Queen re-appears in the main ship, she is once again HUGE.