I would say, revenge against enemies is the main theme. Maria was so angry at her husband for just visiting her kids and ignoring her and then appearing with another woman that she caused the drowning of her kids and then realized what a terrible thing she had done and that is why she cried ie her ghost. La Llorona means a crying woman.
What is a theme from the Mexican myth of La Llorona that still holds relevance today? A. Rejection from loved ones B. Optimism about the future C. Revenge against enemies D. Honesty about living