As far as I can tell the Hopkins trial wasn't a "landmark" trial, except in guest's mind because she won and got a lot of media attention. The gist of it IIRC was that Hopkins mistook someone else for guest, insulted guest for what the other person had done, and then when the error was pointed out, refused to retract or apologize.
I've never seen anything that claims the case established any new precedents in the interpretation or application of libel law. If any legal-minded fraus can add more details, please do.
(guest is also conveniently ignoring that the trial judge had some rather damning things to say about guest's own conduct, even though she won the case.)