Answer:
She opposes the protagonist.
Explanation:
Antagonists always oppose the protagonist.
Think of it as a villian versus a hero or a main character vs conflict.
Answer: Besides changing you topic why don't you explain why you would like to choose art or music. Are you experienced in it? Do you enjoy doing it? Why do you enjoy it? Asking question like these will let you think of good things to write in your research presentation. You could also research on some other people that have made it a successful career and how they started there career and relate to how you would like to start yours that way.
Since its a sibling, and siblings tend to be in a person's close circle of people, informal speech is used.