It's not clear from your question which section of the novel you are referring to. If you are referring to the early parts of the novel, I would suggest that while Antonia's important character traits are probably innate (that is, she arrived in America with them), they are enhanced and developed by the challenging new world in which she finds herself. She has to survive and take responsibility, especially after the death of her father, probably by suicide. She has to work hard, learn a new language, grow up quickly, adapt to changing circumstances, and she does all this with great spirit and cheerfulness, never complaining or bemoaning her lot. Her natural optimism carries her through right to the end of the novel, despite the toughness of her life and even the betrayal of Larry Donovan. She emerges as one of the most attractive characters in American literature.