Since both basically have the same definition. However, "had found" is further into the past. "found" is usually right before the event had happened, or recently. I personally dislike this question since you aren't provided with more information. But since it includes "turned" which is past tense and past participle. C would be the best answer choice.
During her day in the hospital, she never left her daughter’s room. That meant the mother most likely caught bird flu directly from her infected daughter.
