Answer:
So, Mama (Cassie's mom) organizes a boycott of the Wallace store and arranges for the local black families to get credit from a store in Vicksburg, the nearby biggest town. ... And then, Mama gets fired from her teaching position because of the boycott. So that is why she reacted like that towards Sam once he and his father got home.
Hope this helps! also it would have been helpful if you included the reading from the book, ¨Roll of thunder¨.
