...or at least announced their intention to do so. However, truth is a defense against libel and slander.
They would open themselves up to discovery when she fought back. If there is no truth to it, they would have proof and they would do so in a heartbeat. Instead, they're hiding and sending PR flunkies out.
She is not risking her reputation, career, and livelihood on a LARP, not a chance. She is too smart.
Part of a successful suit would require proof that Sidney knows what she is saying is untrue, not just that it is untrue. I don't think anyone doubts Sidney thinks it is true.