That is where the "Joint Intent" disclosure comes into place. If the spouse has not elected to be a party to the loan (Joint Applicant), then yes you can exclude that income from consideration in your underwriting because the income belongs to a non-liable party. Make sure you explain this to the applicant due to a possible adverse action requirement (Denial or Counter-Offer) if she doesn't qualify alone based on her own income.
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The opinion stated here is what it is, My Opinion.