Although at the onset Ona appears to be the complete opposite of Jurgis, she actually is quite like him: Both are traditional naturalistic characters; that is, the typical characters in naturalistic fiction — those who will be exploited. As a naturalistic woman, Ona eventually succumbs to the problems of a capitalistic society, turning to prostitution and eventually dying. Even though she is a stock (flat, stereotypical) character, Ona is the character on whom readers often take the most pity.
Physically, Ona is frail and frightened. She is overwhelmed most of the time. Initially, she is unable to leave Lithuania without her family, so Elzbieta and her children join Ona and Jurgis, as does Marija. This desire to stay with family is a positive trait. In Chicago, she works to keep her Old World order in her New World. Throughout her life in Packingtown, Ona works to keep her family together. She wants both Jurgis and her family to succeed in America, and when his earnings alone are not enough, she gets a job. Like Jurgis, she works hard but is unable to protect and provide for her family.
Ona's representation of the weaker sex is not surprising; in fact, Sinclair uses typical stereotypes. A big surprise, however, is the fact that Ona is able to keep secrets from her husband. In doing so, she exhibits strength of character in contrast to her general weakness. First, her secret actions are a sacrifice for the good of the family. She correctly realizes that Connor has the ability to ruin the family, and therefore agrees to his demands. Second, knowing how Jurgis will react, she keeps the secret of her forced adultery from him. She even returns to work a mere week after giving birth, permanently ruining her health — another sacrifice made by the seemingly frail woman, who supposedly needs guidance and protection from others.
Some readers have difficulty accepting Ona's actions and overall show of strength. For most of the novel she is depicted as being frail and alone. She is the one who Jurgis must protect and care for — a member of the fairer sex who needs a man to provide for her. She's presented in contrast to Marija, who is a strong woman. Ona's actions fit, however, in the greater analogy running throughout the text: In the jungle, a mother fights to the death to protect her young. Ona does what she must — even having an affair with Connor — in an attempt to keep her family employed and therefore fed and sheltered. Even during a time when Ona is being presented as weak and frail, she is actually exhibiting a great strength. It is ironic that the protected, in a way, becomes the protector.
Of course, Ona dies, but before this happens, it is necessary for the system to pressure her into "sexual slavery by her economic masters." Because of the economic slavery, Ona is unable to be an effective wife and mother. This worldview, although consistent with all naturalistic literature, appears in The Jungle to serve Sinclair's purpose of promoting socialism. Ona serves as a negative example for the value of capitalism.