there is no excuse for violations of privacy.
Yes, if I were you I would pursue a lawsuit based on libel. You need to talk with an attorney. Perhaps a cease and desist letter to them.
While I think its pretty shitty what the girl did and pretty shitty the way the elders went to the parents, the information was posted on a public blog. Anyone could see it, read it, print it and share it. Technically I don't think there's a violation of privacy or a case of libel.
Lesson learned: Don't put anything on the Internet that you don't want someone or anyone to see or read.