Before the Bar
I've been on the receiving end of some of the Lumonator's attacks, and it's not pleasant. The trouble is that Motl has no sense of proportion or propriety. He isn't content to attack your logic and knowledge, but seems compelled to go after your species, phylum, gender, education, family, etc.
I still think, however, that using the courts in scientific battles is a really bad idea. I'm not sure how Hossenfelder will fare in EU courts, but I think she would have a hard time prevailing in a US court. She did make herself a very public figure in this debate by writing a New York Times OpEd against the collider, and US courts have a tendency to say that once you have become a combatant, you are fair game. The exception would be if some of Lumo's comments were libellous - that is both damaging to her reputation and clearly false.
In my opinion, Lumo's attacks are usually so over the top that no sensible person would take them seriously enough to damage B.'s reputation. I think she would have been better off to ignore him, but we shall see.