All too often in literature, the theme of the stubborn woman can be put to misogynistic ends to portray women as shrewish, nagging, and chronically unreasonable. Stubbornness in women was not traditionally seen as a virtue in women, especially not among wives, who were supposed to be submissive to their husbands.
Thankfully, this is not how the theme is used in Second-Class Citizen. On the contrary, a wife's stubbornness is seen as a sign of strength, something to be admired. In the figure of Adah, we have a wife who is no longer prepared to be treated like dirt by her controlling husband, Francis, who believes that a woman's place is in the home.
If it hadn't been for Adah's stubbornness, then her children would not have been placed in a nursery, which greatly improves their health and general level of well-being. Francis may well have internalized the notion that Nigerians are second-class citizens in British society, but Adah has not. She knows that she and her children deserve so much better, and she's willing to be as stubborn and persistent as is humanly possible in order to improve their treatment. This also extends to home-life, where Adah shows her stubborn insistence on having a better life by leaving Francis and taking their children with her.