I assume you're asking about "Grapes of Wrath". The Joads are stopped at the California stateline at an agricultural inspection checkpoint. We still have them today. Ma is the only one in the family who knows that Grandma has passed. She pretends that Grandma is still alive and that she needs to get her to a doctor. The inspectors are fooled and wave the family through without making them unload. The reason Ma does this is that she knows the inspectors would not let her transport a dead body across the stateline. The fees and legalities involved in registering the death and arranging for burial, and the delay these would cause, might be too much for the family's dwindling resources and resolution. And so Grandma, in death, is called upon to perform one last service for the Joads.