I think that the characters in the novel represent different aspects that seek to define and redefine modern and traditional notions of the good in India. Koly is the central character in the novel and represents more than a mere girl getting married. She represents the "traditional" notions of Indian girls and their predicament. She also represents the "modern" conception of women in India, who are straddling the world of traditional notion of responsibilities with the modern opportunities for freedom and self definition. Certainly, Koly represents the very best and most challenging of each world and experiencing both with her in the book highlights the complexity of each world.
Raji, the rickshaw driver, also represents a similar reconfiguration of traditional and modern roles. As a man in India, there is much that tradition gives him which would benefit him in his relationships with women, specifically Koly. Yet, he embraces the modern conception of being a man in attempting to win over the heart of Koly through the content of his character and his love for her. Again, this is a modern transformation of traditional roles.
Finally, Koly's in-laws also represent this duality of modern and tradition. The father in law embodies a new sense of a father in law as he cares for her genuinely and teaches her how to read. The empowerment through literacy and authentic love that he shows her is different by the traditional standards of in laws. However, the balance is established with the mother-in-law, whose abrasive and mean spirited ways with her daughter-in-law are praciticed in accordance to traditional notions, where daughter in laws are accompanied by dowry payments and are viewed as "second best daughters." Such treatment is highlighted when Koly is left in Vrindavan, a holy city for its traditional devotee worship, yet serves to be the home for Koly's modern redefinition of self and love.