The answer to your question would be that the antecedent of the underlined pronoun is the following noun: Carol. The fact is that the sentence makes reference to two people: Bob and Carol. This coordinated NP is also the subject of the sentence. As you can see, only one of these nouns refers to a woman (Carol). "She" is the third person personal pronoun that is used to refer to a female, so "Carol" would be your answer.
