depending on your ages and her health, don't.
if you inherit the house, and you sell it the next day you have no tax liability.
if you get the house thru a quit claim deed, the method you are asking about, you are liable for taxes on the existing equity.
depending on your states laws, an internecine transfer is without transfer tax, but call your county tax collector AND assessor.
there is another issue. since you are paying the mortgage already, ask the co about an assumption. just because you own the house, it does not release your mother form the obligation of the mortgage payment.
you need to check with a cpa about your right to deduct the interest payment on your taxes if you aren't on the loan.
as i remember there are some issues that must be covered to get the irs not to challenge you.