need legal advice

Thank you for the prompt reply regarding my inquiries. When I ask my sister about the status of the barangay case she filed against her neighbor (unpaid debts) she said that they were only summoned once after that no summons were sent. I want her to to file a case in the court already because they are harassing my sister everytime they crossed path & also spreading malicious rumor against her which I think should stop because I don't want her children to become affected by all of this things. Is it possible for my sister to file a case? What case should she file? Please help me as I think these people wouldn't stop.

yes, oral defamation