On your mother's tax return you do not indicate that that your mother failed to complete the RMD. Your mother's responsibility to complete the RMD ended with her death and became the responsibility of your mother's beneficiary(s). So the only amount that your mother was required to take was any amount already taken by your mother.
Also, if your mother's beneficiary(s) did not complete your mother's RMD by the end of 2024, they get an automatic waiver of the penalty for 2024 as long as the year-of-death RMD is completed by the end of 2025.
