First, you need to be her legal representative. (Power of attorney, even if you have it, dissolves when she dies.) There will be some procedure in your state to be named her personal representative or administrator of her estate. Then you would file her 2016 tax return. In Turbotax there is a box you can check for "taxpayer died in 2017 but before the return was filed." You will need to print and file by mail. Write "deceased" and the date at the top of page 1, and sign the back in your own name plus "personal representative."
Then you will also need to file a 2017 return for any 2017 taxable income she had before she passed.
