Little bit of a legal issue..?

Here goes. My wife's brother abandoned his wife and his kids for another woman. My wife got very upset (she's been in pain from complications involved with wisdom teeth removal and has been on narcotic painkillers). Anyway, she made some derrogatory comments on the girl's Facebook page in anger. One of the comments may have involved the words "if i find out it's true, i'll kill you". Now the girl's mom is involved and says she's getting the authorities involved. What are we looking at here? Jail time, lawsuit?