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Yes - if your domestic partner is listed on the title as a legal owner of the property - she is eligible to deduct mortgage interest she paid during 2015.
However - the IRS will do verification and will compare deductible mortgage interest with the amount reported on form 1098.
If your domestic partner will simply report mortgage interest deduction - it is possible that the IRS would send a letter asking for supporting documents.
To avoid such situations - I suggest to attach a note to the tax return with explanation of facts and reasoning.
Let me know if you need any clarification this matter.