Although it's not necessary to meet LICO (minimum income threshold) to sponsor, and it's not even necessary for the sponsor to have a job, my understanding is that CIC still wants to see some source of income, as long as it is not social assistance (welfare, or Ontario Works as it's called in this province). If your wife is receiving EI, a pension, disability benefit, or interest from investment, savings, etc? Any of those would be acceptable proof.
BTW, does anyone know if it's absolutely necessary to always use the most updated forms? CIC is constantly 'updating' its forms, without saying what the 'changes' are. For example, the Sponsorship Agreement/Undertaking form IMM 1344 dated 04-2013 looks identical in wording to the one dated 12-2012. Ditto for the Generic Application for Canada IMM 0008. Whatever the differences are, they must be extremely minor, like a punctuation mark or something! It's not a big deal to re-enter the same info on a new form on the computer, but it is the signature pages which concerns me. Does CIC expect the sponsor to tell his/her spouse to fax/scan another signed page which shows the most recent update in the bottom corner, or will they accept the already-signed page from the previous version? In both cases, the wording on the signature pages is the same. It's a nuisance to have to do this, especially when the sponsored person overseas doesn't have convenient access to a computer/scanner/fax machine.