"Claudia," I said patiently. "When one is eighty-two years old, one doesn't have to learn one new thing every day, and one knows that some things are impossible." (9.254)
Claudia just got told what was up, which is fitting since Mrs. Frankweiler's 82 years on earth totally trumps Claudia's meager 12. Claudia may think that she's the smartest all the time, but Mrs. Frankweiler can give her a run for her money.