Went thru this in the UK. If similar here, you will need to apply for a mortgage based on your income and go through some limited conveyancing to transfer the deeds to your name. All costs money, solicitor and valuation fee from mortgage company, plus the fact that it will be a new mortgage means you may be charged a higher rate of interest.
Don't go for just her leaving and you taking on the mortgage unofficially, later in life you will have a pain in the ass trying to get her name off the deeds and she will continue to be entitled to a portion of it, until you do.