Why does big ma park her wagon at the back of the field? How does Cassie react to this and what does her reaction tell us about her

Ma has to park the wagon "away" from the entrance because the spots closer to the entrance were reserved for the store's white patrons. Blacks were not allowed to park in front on the entrance. Cassie cries that this is unfair but Big Ma insists that they need to pick and choose their battles.