I was just finishing this when @dmertz posted:
@fanfare - assuming the IRA owners dies after the age of 72 (which occured in this case),the non-spouse beneficiaries must fulfill the same RMD obligation in the year of death. I am not aware that the proposd rules impact the RMD in the year of death. I thought that since the rules cover owners who died after 12/31/19, then it's those that passed in 2020 is where the confusion lies as it pertains to 2021 (not the year of death) RMD.
@bmwermuth - this would be a good article to read. As you state there were 4 beneficiaries, did any of them take the RMD in 2021? Remember "RMD" mean the required minimum distribution, but it can be more than that. If one of the other 3 cashed in part of their inherited IRA, that could satisfy any RMD requirement you wife may otherwise have.
https://www.irahelp.com/slottreport/year-death-rmds
The owner's 2021 RMD requirment was
1) the balance of the IRA on Dec 31, 2020
2) divided by either a) 12 if the father had his 89th birthday in 2021 or b) 11.4 if the father was to have his 90th birthday in 2021
3) equals the 2021 RMD requirment.
That RMD can be satified by the owner taking some or all of the RMD before passing OR some or any of the beneficiaries taking distributions in 2021 that equalled or exceeded 3) minus what the owner already took. So even though your wife didn't take any RMD from this inherited IRA in 2021, how about the 3 others? how about dad? did they? and did the sum of those distributions exceed 3)? that could solve your 2021 problem......
https://static.fmgsuite.com/media/documents/62a03f4e-4470-466d-ab38-c2d1850bfc7d.pdf
