It’s perfectly appalling to think of being twenty, Marilla.
But that night, when Marilla went to bed, acutely and miserably conscious that the little gable room at the end of the hall was untenanted by any vivid young life and unstirred by any soft breathing, she buried her face in her pillow, and wept for her girl in a passion of sobs that appalled her when she grew calm enough to reflect how very wicked it must be to take on so about a sinful fellow creature.
There are no more uses of "appalling" in the book.
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The live in appalling conditions.
She has scheduled a news conference to respond to the appalling accusations.