At first glance, Isabella seems to exist as a foil to Catherine Earnshaw. Unlike the strong-willed and free-spirited Catherine, Isabella is delicate and conventional in her behavior. However, as she gets older, she shows more stubbornness: Nelly describes her as “possessed of keen wit, keen feelings, and a keen temper, too if irritated.” To everyone’s surprise, Isabella falls in love with Heathcliff, and she insists on pursuing him even though everyone tries to warn her away. Her brother “shrank forebodingly from the idea of committing Isabella to [Heathcliff’s] keeping,” and Catherine warns her that “he’d crush you like a sparrow’s egg.” Even Nelly urges Isabella to “banish him from your thoughts.” However, Isabella shows a surprising level of defiance and independence in marrying him in spite of the opinions of others. In this sense, she is wilder than Catherine because she is willing to defy social convention and marry a man with no family and connections.
Isabella, however, pays bitterly for her stubbornness and naivety. After she elopes with Heathcliff, Edgar declares her to be “my sister in name only.” What’s worse, she almost immediately regrets her hasty marriage, writing to Nelly, “Is he mad… is he a devil?” Isabella is so unhappy with her husband that when Hindley reveals his plan to murder Heathcliff to her, she is tempted to go along with it. Ultimately, Isabella’s moral judgement triumphs, and she warns Heathcliff of the attack. But she later admits to Nelly that she takes pleasure in watching Heathcliff suffer: “his weakness was the only time when I could taste the delight of paying wrong for wrong.” Perhaps to protect her unborn child or perhaps because she is afraid of becoming morally depraved due to her bitterness, Isabella flees Yorkshire and never returns, living in London while estranged from her husband. This decision further reveals how a seemingly fragile character is actually a strong-willed and independent-minded woman, unafraid to take changes and follow her own heart.