The given sentence is in the passive voice: ``Then her face was bowed." In passive voice, the subject receives the action, whereas in active voice, the subject performs the action.
- Option A: ``Then she was being bowed her face" is incorrect as it does not form a proper structure in passive or active voice. The use of ``was being bowed" is not appropriate here.
- Option B: ``Her face was bowed by them" is correct in passive voice but does not express the active voice as required by the question.
- Option C: ``Then she bowed her face" is the correct transformation into the active voice. Here, the subject ``she" performs the action of bowing her face.
- Option D: ``Then her face has been bowed" is in present perfect passive, which is not the correct tense for the given sentence. Thus, the correct answer is Option C.