TurboTax is likely actually asking if her brother opened a Roth IRA before 2021; the date that the inherited IRA for your sister was established is irrelevant. The date that your sister might have first opened her own Roth IRA is also irrelevant to the taxation of this distribution from the inherited Roth IRA.
(I wouldn't be surprised if TurboTax mistakenly asks if "you" opened a Roth IRA before 2021. Lots of questions in the retirement section have been messed up by developers this year (2025) in the process of transitioning to an updated user interface.)