It Could Have Been Oxygen Deprivation

Mrs. Gutierrez also thinks that she had probably suffocated to death within the coffin since she had been buried inside for over a day. Although she attempted to fight her way out, there was just no chance of her clawing her way out of the tomb and slowly the lack of air inside is what had led to her death.

She Looked Like She Was Sleeping

Her family would even share that when they had finally gotten her out of the tomb after hearing her screaming, she just looked like she was asleep. Her body temperature felt warm to the touch and there was no horrible smell emanating from her.