Answer:
mitigate her damages.
Explanation:
Mitigate is the act of reducing or making less. To mitigate damages means the way a plaintiff reduces injury by taking certain steps. When a contract is breached to wronged party is expected to take measures to reduce harm.
Valerie can take any action that will prevent erosion on her land. So to avoid additional loss she can for example hire another person that will be able to build a stone retaining wall to prevent erosion on her land