I believe that choice B. is the only one that when applied to the sentence will make it grammatical and acceptable, i.e., "correct." This means that as it stands the sentence is ungrammatical--and therefore choice A., "no change," has to be ruled out--since the relative (or adjective) clause which by being one of a Latina living outside the mainstream is incomplete because it lacks a conjugated verb (which by definition every clause must have) that would be "governed" by the clause's subject which; cf. grammatical examples like which by being one of a Latina living outside the mainstream resonated or which by being one of a Latina living outside the mainstream stood out.
Choice C. would not be correct since the resulting sentence, Her voice, being one of a Latina living outside the mainstream, it found a large and attentive audience in 1984, contains a redundant it trying to serve as the subject of the main clause whereas the sentence already has a subject, Her voice, even though this is separated from the main verb found by the participial phrase being one of a Latina living outside the mainstream.
Finally, applying choice D. would also not result in an acceptable sentence since the subject it of the relative/adjective clause in which it was a Latina living outside the mainstream would then not have any clear referent in the sentence as a whole, i.e., Her voice, in which it was a Latina living outside the mainstream, found a large and attentive audience in 1984. That is, it would be which, not it, that would refer to Her voice which is modified by this relative/adjective clause.