Inherited Roth IRA from my mother. 1099-R box 7 lists distrib code T. If I call it an inheritance, TurboTax asks when she first opened the Roth. What if I don't know?

I don't know if she opened the Roth before 2014 or not. If I answer that she opened it after 2014, Turbo Tax needs more info about her initial contributions that I don't have. I *AM* supposed to say that it's an inheritance, right?