Well, last fall, the sorority actually won its lawsuit in Washington state court — by default order, since the post was anonymous, and no one came forward to claim the post and defend the case.  The legal theory was that the comment was a breach of contract (on the theory that the anonymous commenter had been a sorority member who had promised to keep the secret); a breach of a duty of confidentiality (basically duplicative of the breach of contract theory in this case, I think); a misuse of confidential information (likewise duplicative of the breach of contract theory in this instance); and an invasion of privacy (an unsound claim, since organizations don’t have privacy rights: there’s a Washington case on that).  The court accepted the plaintiff’s theory, which is unsurprising given that the defendant didn’t show up.