First, go over your entries and make sure they are correct.
The IRA could have been a non-deductible IRA will all contributions made with after-tax money or a qualified distribution from a Roth.
Please note: A qualified distribution from a Roth IRA is tax-free and penalty-free, provided that the five-year aging requirement has been satisfied and one of the following conditions is met:
It was not a Roth IRA, and the contributions were all pre-tax. But regardless of how I answer TT's question "Did you have nondeductible contributions for this IRA?" the amount does not show up in my taxable income.
I also made a non-deductible contribution to my own IRA this year and in past years. Looking at the form 8606 (Non-Deductible IRAs) that TT created, it seems to be treating this distribution from my mother's IRA as if it were a distribution from my own IRA. My IRA distributions would not be taxed, because all contributions were made after-tax. I did tell TT that this 1099-R was from an IRA I inherited, but it doesn't seem to be separating the two.
The IRA distribution from your mother's pension would be taxable if they were never taxed to her.
I would suggest you delete the form 1099-R entry in TurboTax and re-enter it and make sure you treat the questions in TurboTax literally before you answer them.