You can treat the home as a second home and report interest on schedule A. However, since you are 'maxed out' on the interest deduction on your main home, this may cause your total interest deduction for both homes to be less than the interest deduction for the main home by itself. Depends on how large the average loan balance is and how little the amount of interest paid is on the second home is. Keep in mind both 1098's are sent to the IRS.
I don't know much about rentals but if you are not collecting rent and your mother is living in the second home, seems like a stretch to qualify it as a rental.
