As the title of Book IV suggests, this section of the book is all about the different fates of the three pioneer women explored in the novel: Lena, Tiny and Antonia. The three women have enjoyed very different fates: Lena has gained a measure of independence that impresses the narrator, Tiny has made lots of money through the gold rush and various means, and poor Antonia is living the life of a slave, working for her brother having been abandoned by Larry Donovan. The women's fates are very strongly contrasted, and the story of Tiny in particular, which is juxtaposed to the fate of Antonia, highlights the different kind of fates that pioneer women could experience. Note how Tiny is described as she narrates how she lost three toes to Jim:
Tiny mentioned this mutilation quite casually--didn't seem sensitive about it. She was satisfied with her success, but not elated. She was like some one in whom the faculty of becoming interested is worn out.
A further comparison between Tiny and Antonia is the way that Tiny seems to be so grim and unable to enjoy life. Although she has gained considerable wealth, this has been at the cost of her three toes nad the ability to be satisfied and enjoy happiness. This is of course in contrast with Antonia, who, no matter how much suffering she has endured, still is able to take pleasure in living and allow her spirit to enjoy the freedom that perhaps her body is not able to experience. A good thesis statement on this section of the novel therefore might be something along the lines of:
In Book IV of My Antonia, the different fates of various pioneer women are presented in order to foreground the fate of Antonia.
This thesis statement would allow a comparison and contrast between Antonia and the other two women and a more detailed discussion of their presentation relating to the central themes of the novel.