It took her another 36 minutes before she called emergency services.
Matthew was taken to hospital where he died hours later.
He weighted only 84 pounds (38kg), and was severely malnourished and dehydrated.
Matthew also had several injuries, including multiple cuts and bruises.
The medical examiner said the cause of death was "fatal child abuse syndrome with dehydration and malnutrition".
According to police, Tirado screwed cabinets shut and locked the refrigerator.
Matthew was forced to dig through rubbish for food and drank oils and condiments.
Her lawyer, William O'Connor, said the mother was struggling with her own mental health issues.
"She is very remorseful. She does grieve," he said.