Of course, she will have to report no income on her own I-134 if it is true. Your US fiance is your primary sponsor, and she must submit her own I-134. That's why most consulates allow a joint sponsor....who must submit a separate I-134. As I stated joint sponsors MUST be US citizens or Green Card holders who live in the United States. If they are not US citizens or Green Card holders living in the US, their income is irrelevant.
What is a K-1 Joint Sponsor? (boundless.com)