The article says that she denies writing that exact comment and that is in fact part of why the lawsuit has been permitted to go forward.
The court called her allegations "plausible" (though that's a far cry from "true"), and the article also says that Benton posted an apology: "By revealing such details without making an effort to contact her and seek confirmation and explanation, and otherwise adhere to rigorous reporting methods, the tweets did not meet Nieman’s journalistic standards. I apologize and regret my error in judgment."
So it seems to me that Benton has already admitted failing to validate this information, thus I'm reluctant to take it as given.
That aside, if comments here are any indication, she's screwed even if this isn't true. Half of the posters here appear unaware that she denies making that comment.
Comments like those can be used as evidence of damage to her reputation should she win.
Do you have insider information about the case, or is this your synthesis? The former strikes me as being unlikely, because you seem to have missed that the cornerstone of the suit is the claim that she's not actually the one responsible for the anti-Muslim comment, which is what makes this defamation.
The underlying issue for the university is whether she can effectively teach Muslim students when she thinks they're "scum" who should be deported. And, will Muslim students be comfortable signing up for her class now, or has she effectively steered them away with her racism? Regardless of how it came to their attention, the university undoutedly has some kind of zero-tolerance policy against racism.
Generally I agree with your sentiment, but I think this case squeezes into that small "little to zero" impact section.