Suing her wouldn't be the problem. Actually serving her would be.
Yeah, suing her would have been overall difficult.
For one thing, her original tweet didn't mention Vic by name, except in a second tweet, which was just a screenshot of something that
someone else said:
archived 20 Jan 2019 22:01:10 UTC
archive.md
Vic's lawsuit would have had to establish that she was talking about him in the first tweet, and/or that her second tweet was actionable defamation on its own. That could probably be done, but it complicates the argument.
Second, she was just a random Twitter handle; her dox wasn't known until a couple of months later (based on when the dox were archived, that'd be March 10... she apparently didn't have a thread until July 2, though). Vic would have had to sue her based on a pseudonymous Twitter handle, and probably would've had to obtain discovery from Twitter to actually track down her real identity... I'm not sure if the farm's efforts in compiling her dox would have even been usable for proving who she was in a legal context. I suspect probably not.
Third, it's unlikely that her tweet would have done any damage on its own. She was a literal nobody, some random ass-mad fujoshit, bitching about someone who ass-mad fujoshits had been bitching about for a decade because he wouldn't sign their gay incest child porn artwork. She could've argued that she wasn't really responsible for the harm to Vic that was primarily caused by other people, who had more relevance and credibility, picking up the accusations of sexual misconduct and blasting them to much larger audiences.
And of course, let's not forget that she probably has no money and nothing worth taking. Suing her would have been a purely symbolic gesture.
Pretty much every aspect of trying to sue her would have been complicated.
edit: it would've also been much harder to show actual malice, just in case Vic ends up being ruled a public figure of some kind.