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.
since you are a legal owner of the real estate the IRS allows a deduction for the mortgage interest even though you are not directly liable for the debt. however, there are rules. Mortgage payments and taxes paid from a joint account with two equal owners are presumed to be paid equally by each account owner (absence evidence to the contrary). However, if payments are made from separate funds, each taxpayer is entitled to deduct all the interest and taxes they pay with their separate funds (CCA 201451027).