Worrying about the business has turned her into a nervous _________ .

The correct word to fill in the blank in the sentence "Worrying about the business has turned her into a nervous _________." is "wreck". This is because the context of the sentence implies that the concern over the business has had a negative impact on her mental state, causing her to become extremely anxious and distressed. The word "wreck" in this context means a person who is in a state of extreme distress or disarray, which fits the intended meaning of the sentence.3