What can my friend in M do about the harment to her family by family in Maine?

a friend of mine living in m has a 16 yr old daughter that was visiting her grandmother in Maine last year and refused to come home. They listed her as a runaway but when the authorities went to the house the grand parents refused entry and the girl ran out the back door. There has not been any abuse it is basically a case of greener gr. My friend has come to terms and is allowing the girl to stay. However the family in maine continues to har them in m by posting obscenities on web pages and pointless phone calls to say hurt-full things. They have tried to ignore anything that doesn't pertain to the well being of the 16yr old. But today a letter addressed to her younger 12yr old daughter was received. It was a very vulgar letter demeaning the parents and other grandmother. Im talking really offensive slander. Including telling the little girl that she and her little brother were going to end up in an orphanage. What can they do about this?