How long does Miriam keep herself shut inside the house after her attack in the novel, Whispers Through a Megaphone?

Miriam shuts herself inside the house for three years. In her mind, she does this to protect the world from herself. When she attacked the man in the woods, scratching at his eyes, she frightened herself. Her home was the natural self-imposed consequence. Miriam felt she deserved to be locked up within the place that initially removed her from the world.