why is Cassie angry with bigMa

Mr. Simmons demands that Cassie apologize to his daughter, although Jeremy insists she already did. Cassie tries to run away and is met by Big Ma. Mr. Simms demands that Cassie say "I'm sorry, Miz Lillian Jean," and Big Mama reluctantly makes her comply. Cassie says it and runs crying into the wagon, thinking this is the cruelest day that she has ever endured. She is angry at Big Ma for making her apologize.