As I see it stabilized for the first time, the choreography makes sense.
Shatner is in the forground, along with deflector light; Nichols is in the background with the red alert light. Both move stage right, towards the lights. Everyone else moves stage left. The arc light flashes and then all the lights go out -except for the deflector and the red alert lamps, which flash for a second or so, before cutting to a shot of the ship at an angle.
I've always found this scene to be very effective in showing how devastating the Romulan plasma weapon was. It was the first time the bridge was shown completely without illumination, except for those two key red lights. The blocking of the action only served to draw the viewer's eyes to those points.
And now that the shot was presented horizontally (thanks to the OP) , I understand why Nichols had her arm in that awkward position. She appears to be feeling for the frame of the alert light, ensuring that she wouldn't block it out, and thus ruin the plan of the shot.
The laws of physics can be broken, or at least suspended, in service to the director's sense of design.