"The Traditional IRA (Acct #1) the $8,000 was distributed from is in her name and grandmother's name + (Decd). There were no contributions to this account. Basis is $50,104"

Then you do enter this into the 1099-R worksheet, because basis divided by total FMV is going to give prorated percentage for portion not taxable and portion taxable of the Gross distributed.

"The $8,000 is an RMD."

It falls under the 10-year rule. Not Grandma's RMD.

"The 2021 $6,000 contribution made on behalf of the taxpayer was a different account - a Roth IRA (Acct#2) only in the taxpayer's name."

Has nothing to do with the story for the inherited account. I think you confused Source of money, with IRA provisions. These provisions do not apply to anything in this scenario. There is no Relationship between Inherited IRA and your taxpayer's own IRA(s) and activities.

No rollover.

No conversion.

No Backdoor.

No transfer.

No trustee-to-trustee event.

Just a paperless movement of Distributed money to be deposited into some account your taxpayer owns.