I think that Whelan's work can classify as historical fiction. It is a story of what many girls in India have to endure, and while it might not be specific about one person, it focuses on a historical and social condition. It is here where the work makes the strongest statement about a social condition in India, and for this, it operates quite well as historical fiction. Additionally, I think that the realistic details of life in India are conveyed through a fictional character. Koly might not be necessarily real. However, the conditions and situations that she faces, the fact that she goes to Vrindavan and finds hope, and the idea that her life takes different turns in different parts of India are all real events and accurate. Another representation here could be the genre of young adult fiction. Koly proves to be a protagonist that could be appealing to young people, particularly girls, as she speaks for a condition of being young, something that is not openly accepted in India. In this, her story can also operate as a bildungsroman, an essential ingredient in Young Adult Literature.
It's a realistic fiction book, believe it or not, this can happen in India today. It's most likely that Koly is not real though.
p.s I'm Indian