Tools of Characterization
Nnu Ego remarks at one point that it is a joy to wear worn clothing. As a mother, she can rejoice in the fact that she has children and can't afford new clothes, whereas the women with new clothes are less likely to be blessed with a lot of children. But clothing marks other kinds of status as well. Nnu Ego struggles with poverty, even while she's dependent on her lazy husband. Her junior wife Adaku is able to dress well after she becomes an independent woman. We learn that the "virtuous" woman (as perceived by society) is more likely to wear shabby clothes.
Because Nnu Ego is the first wife and then the senior wife, she clings to traditional values, and struggles throughout her life with poverty as a result. Adaku, as junior wife, gets sick of being mistreated, and realizes that her social position means she's nothing. Adaku asserts her independence from men and is able to create her own wealth.