Learn French: La situation était difficile, mais elle ne l'avait pas rendu vulnérable. - The situation was difficult, but it hadn't made him vulnerable.

When expressing "to make [someone/something] [adjective]", French uses rendre, not faire. You use faire when it is followed by an infinitive verb, as in faire pleurer (to make someone cry). Because vulnérable is an adjective describing a state, rendre is required.

Since the subject elle is feminine, why isn't the past participle spelled rendue?

In compound tenses using avoir, the past participle doesn't agree with the subject; it agrees with the direct object, but only if that object comes before the verb. Here, the preceding direct object is l' (meaning "him", masculine singular). Therefore, rendu remains masculine singular. If l' had meant "her", it would be spelled rendue.

Why use the plus-que-parfait tense (avait rendu) rather than the passé composé (a rendu)?

The plus-que-parfait (translating to "had made") is used to describe an action that happened before another past point in time. The situation being difficult is an ongoing past state described in the imparfait (était), so the writer is emphasizing that up to and during that time in the past, it had not made him vulnerable.

Why is the pronoun elle used if the English translation says "it hadn't made him vulnerable"?