I want my girlfriend to be able to write off mortgage interest on her taxes but i'm the only one on the loan. Can she do this or do i need to refi/add her to loan?

I'd like to split the mortgage interest amount that can be written off between me and her.  But she isn't on the title or loan.  Refinancing is expensive and I'd rather just cut the amount I claim on taxes and give her the balance but am not sure if that's allowed.  I don't want her to just do it only to find out she's submitted bad taxes.