How is the lending institution report going to read? Normally she would be the sole name listed and her SocSec number which is what the IRS receives. That complicates the answer that you are probably seeking.
The safe way is for her to take the benefit and you two agree how to handle the benefit in proportion to how you two divide the payments.
If I were in your position, I and the other would see a tax attorney mortgage..money well invested.
She is essentially the only one eligible for the tax benefit as the lender's report only lists her social security number.
