Final answer:
The appropriate indirect object pronoun for the sentence 'A Rocío y su madre, les duele la cabeza' is 'les'.
Step-by-step explanation:
The appropriate indirect object pronoun for the sentence 'A Rocío y su madre, les duele la cabeza' would be les. The pronoun 'les' is used to indicate that Rocío and her mother are the recipients or beneficiaries of the action, which in this case is the headache.
Indirect object pronouns are used to replace the noun that receives the action indirectly in a sentence. In this case, the headache is indirectly affecting Rocío and her mother.
Here is an example to illustrate the use of the indirect object pronoun 'les':
Les compré un regalo a Rocío y su madre. (I bought them a gift for Rocío and her mother.)
Learn more about Indirect object pronouns in Spanish