The third point of view:
Isabella was right, the panic room was located in Maya's room. The moment they had entered, the dust and cobwebs launched a full onslaught on them - showing nobody has been there for a long time now.
It was obvious to Isabella that her father could have had the room cleaned but he must have kept it intentionally this way - what were the chances Miguel would think of a secret room in this kind of dirty place? They would turn back right away.
Finding the entrance might be hard for others but Isabella has lived with her mysterious father for years and knows how his mind works. With the kids watching, she squatted down beside the bed and started feeling around for something.