Have they tried reporting the incident to Facebook already? Facebook has a review function now that allows facebook officials to review a certain post and remove it as the case may be.
Where is the victim located? If the victim and the perpetrators are located in another country, then that is where the victim should file a case against them since that is where the alleged crime was committed. Of course, it depends if the country has cybercrime laws that is applicable to your friend's case, and it also depends if the lawyer who will handle her case deems that there is sufficient evidence for the case to prosper in court.
Your friend should seek the advice of a local lawyer in the country she is currently working in.
Good luck, and may your friend's efforts yield positive results.