If the money in your dad's IRA was transferred to your mom's IRA trustee-to-trustee, that was a nonreportable transfer. That money in your mom's IRA is now treated as if it had always been in your mom's IRA. Indicate that the RMD distribution was not from an inherited IRA and was not rolled over.
(If you indicate that the distribution was from an IRA inherited from a spouse and you indicate that the distribution was rolled over to the IRA of the surviving spouse, TurboTax will report it as a nontaxable rollover of the entire amount.)
