Why does Cassie decides to get revenge on lillian jean in roll of thunder hear me cry?

Cassie decides to get revenge on Lillian Jean because she is fed up with the injustice and mistreatment that her family faces from white people in their community. She is standing up for herself and refusing to let Lillian Jean continue to humiliate and disrespect her. Cassie ultimately wants to assert her dignity and challenge the racial hierarchy that oppresses her.