Furiosa doesn't need orders to react to an imminent threat. The airlock being forced open with no attack coming from the open ramp would seem to confirm Harley's fears about their attackers wanting to force them into the open, and Furiosa swivels slightly when it becomes clear the ship is breached, a few steps away from the others but still within the circle of light. She turns toward the attack, because she and Harley are the fighters here and there is no choice but to respond to a threat, but she tries to keep the ramp in her peripheral vision as well.

There is nothing to be seen in the surge of shadow coming toward them, but the sounds tell her many, fast, sharp, and above. Her mind's eye constructs something fancifully like tremendous scorpions, all blackness and claws. It hardly matters how accurate that image is in reality. Envisioning something threatening yet familiar makes this situation somewhat less overwhelming.

Even before the droid speaks or Harley gives her orders, Furiosa has aimed her pistol and pulled the trigger twice. She can't afford to waste ammunition if it has no effect, but shooting at the shadowy mass while it's down the hall from them is the only time she can use a ranged weapon without fear of hitting the people around her.

Once the two rounds fly, though, their attackers are too close and Harley is telling them she'll cover them, so Furiosa reaches out with her metal hand and drags Palmer a little closer, heading for the ramp obediently. "Head down! They're on the ceiling!"

Okay, she's only guessing it's a 'they' and they're on the ceiling based on sound, but the last thing she wants is to watch something reach down and grab one of them by the neck.