Ah, that's how an excess contribution to the Roth IRA occurred and EJ handled the correction properly. If the RMD for that traditional IRA was not first satisfied by a distribution from a different traditional IRA of your mother's, the first amount distributed from the traditional IRA that was converted to Roth was the RMD for that traditional IRA that was not eligible for conversion to Roth. Because it was not eligible for conversion to Roth, it became an excess contribution in your mother's Roth IRA. That excess remained in the IRA when it was transferred to an inherited Roth IRA for your benefit, so it's proper that it was distributed to you as a return of excess contribution.
When preparing your own tax return, simply enter the Form 1099-R as received. There is no need for TurboTax to know if the distribution was from an inherited Roth IRA or not.