Final answer:
The main conflict in this scenario is Cassie beating up Lillian. So, the correct answer is option 4.
Step-by-step explanation:
The main conflict in this scenario is Cassie beating up Lillian. While each of the other options (Cassie becoming Lillian's servant, Lillian telling Cassie her secrets, and Cassie demanding an apology) contribute to the story, the act of Cassie physically harming Lillian represents the peak of the conflict and the most significant action. It is this violent act that creates the most tension and has the greatest impact on the relationship between the characters.
So, the correct answer is option 4.