The Reality of Choices and Seeking Divine Help

Salam, everyone. My sister ended her marriage after facing some really tough situations. Her former spouse was involved in haram activities like using and selling drugs, and he even caused her physical harm, leaving visible injuries. On top of that, his mother, who has a known history of misconduct and immoral actions, is now spreading false rumors in our community, claiming my sister was at fault instead of him. It’s been heartbreaking to see. What happens to people who spread such lies in this life? And what can we do about it? Are there any specific duas or prayers we should turn to for guidance and protection?