Why did Kiara's mother go to prison?

Kiara's mother went to prison because she was supposed to be watching Kiara's sister, Soraya, and the little girl got out of the apartment, fell into the swimming pool, and died. When Soraya was missing, they found Kiara's mother, Cheyenne, in the bathtub with her wrists slit. She got negligence and a couple of years in prison instead of being locked up for the rest of her life.