Ness opens her mouth to say something appeasing, something about how Clarisse clearly has social skills that Ness simply couldn't trust herself to employ without having done the research first,

but then the rest of the sentence processes and she's too shocked to worry about smoothing any potentially ruffled feathers.

"Haven't read—not any? Not at all?"

That not everyone loves to read is something Ness is conceptually aware of, but that they might not read at all—

"Were you never taught to?"

That's the only reason someone wouldn't read at all, surely, is if they couldn't.