Answer: She must use the money to buy her own clothing.
In "Incidents in the Life of a Slave Girl," Jacobs tells us that her grandmother was a great cook. Her crackers were famous in the neighborhood and she was allowed to bake them at midnight in order to sell them. However, she was only allowed to do it provided she would clothe herself and her children from the profits. She saved a little bit each year, hoping that this would allow her to eventually buy her children.