Siren (video game)/Fridge

• Fridge Logic: How would Howard and Melissa know that downing a brain shibito would knock out the spider shibito for that particular stage? It doesn't really make sense, especially when Melissa follows the wheelchair brain shibito and the (very) creepy shibito nurse into the lift for the sole purpose of knocking brainy out. Why would she do that? Why? Isn't she 1) preoccupied with finding Bella and 2) crapping herself?