Here is the information on filing your mother's return. TurboTax does not support the 2848 form but it can be downloaded from the IRS site.
Form: https://www.irs.gov/pub/irs-pdf/f2848.pdf
Instructions: https://www.irs.gov/pub/irs-pdf/i2848.pdf
You would have to physically sign a paper return and mail with the attached POA.
