What is the uk military take on libel slander?

To cut a long story short, X and Y, are in an ongoing court case (together not against each other). In this court case Y's sister, Z, is is acting on the defence side as a witness but all based on hearsay. Even the courts were confused as to what and why the case against X and Y is all about. Outside of this but during, the sister, Z, committed libel slander via facebook against X and Y and then later removed it, however they had already received the email from facebook saying this person has posted on your wall, and showed what was written. In terms of the court case, Z will be blown out and discredited. But, she happens to be in the Army, and we're wondering what the army's take is on such behaviour should the facts and evidence be forwarded?