What level of income, if any, must I show, for my Green Card holding wife to qualify for Naturalizaton?

Level of income is not a requirement for a naturalization application. Tax returns are required for naturalization interviews not for the level of income earned per se, but to determine other factors such as whether persons are paying taxes on the money that they earn, whether joint returns are being filed where the applicant received the green card through marriage to a US citizen or permanent resident, or if the applicant worked with the sponsoring employer after obtaining the green card, etc. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.