Answer:
duty of loyalty
Explanation:
The duty of loyalty is probably the most fundamental duty that an agent must respect since the agent should always act in the best benefit of their principal. The agent should also avoid any type of conflict of interest between himself/herself and the principal. In this case, Stella benefited from private information and instead of making her principal purchase the land for a cheaper price, she made her sister do it and then resell it for a large profit.