Amb. Yovanovitch may wish at some point to consult a good lawyer about a civil lawsuit against Giuliani for, among other things, defamation (including both slander and libel), and tortious interference w/ contractual relations (her employment w/ DOS).
Giuliani's a private citizen, not clothed with whatever sovereign immunity or other protections public servants like Volker and Sondland may enjoy. Not clear how she'd proceed vs. her employer, DOS, for what in a civilian context would look like a constructive dismissal,
but I'm sure she has recourse available under existing government labor relations procedures. While I think it unlikely she'd battle DOS, going after Giuliani would be very much in the public interest (to deter future such baseless and political attacks on our diplomats).
Trump, of course, has also defamed Amb. Yovanovitch (calling her a "bad person" and tweeting that disasters have followed her throughout her career), but he enjoys absolute immunity from civil complaints for actions taken in his official capacity as POTUS.
