Answer:
The correct option is c- her.
Step-by-step explanation:
Objective pronouns are one of the two main groups of personal pronouns. Specifically, the group that refers to the object of the sentence. Or in other words, the pronouns that receive the action in a sentence.
In English grammar objective pronouns, which include me, you, him, her, it, us, you, and them must follow the verb in a sentence, becoming them into the recipients in sentences.
Bearing in mind the explained above, it could be said that the option that better complete the sentence is option C. her, resulting in "I left instructions for Damon and her" since both Damon and her are the recipients (objects) of the verb left.