One of the main themes Cushman chooses to use in this novel is freedom, though some may argue that it is obedience. This thought is not true, considering the fact that Catherine was never once obedient to her father. Cushman illustrates this theme using Catherine's birds.
I think the answer is C, irony, because the quote is definitely not imagery nor anecdote, and it is not making reference to a famous literary work, idea, nor person, eliminating the choice of allusion as well.
Non-literal
she’s not actually the not sharpest tool, she’s not smart
she’s nice, not actually tasting sweet
she’s never angry, her bones can’t have anger
I think it a or b but think more a sorry if I am wrong