Final answer:
Clothilde should refer to Chapter 10: Herbs for Respiratory Conditions to find an herbal therapy for her niece's chronic cough as it deals with herbal remedies for respiratory issues.
Step-by-step explanation:
Clothilde should consult Chapter 10, titled Herbs for Respiratory Conditions of the 'The Big Book of Herbs and Herbal Medicine' to recommend an herbal therapy for her five-year-old daughter's chronic cough. Respiratory conditions typically include ailments such as coughs, colds, bronchitis, asthma, and more, all of which affect the respiratory system.
As the chapter deals specifically with respiratory issues, it is likely to provide the best guidance for choosing suitable herbal remedies that could alleviate symptoms or provide relief.