If your mother passed after 1 January 2020, then she is eligible to receive the Recovery Rebate Credit on her 2020 tax return. Since you returned the stimulus check you will enter zero in the box for that payment. In all likelihood, her return will be showing a refund due.
See the question "Will a deceased person receive payment?" in this link.
My spouse died in 2020. I received a $600 stimulus payment but he did not. Even though he was deceased, I thought the payments were based on 2019 tax returns. I don't know how the IRS would know he was deceased unless they were somehow notified by Social Security. For 2020, I am filing a joint return as surviving spouse. I indicated (in TurboTax) that I received $600. The program automatically says that I will receive a credit of $600. I don't think I should receive the credit. What should I do?
Yes you still get the second 600 for him. Did you get the full 2400 for the 1st one?
For deceased individuals see the first 2 questions under Eligibility. If they died in 2020 they still get it.
https://www.irs.gov/coronavirus/second-eip-faqs
Thanks. Yes, we got the full amount of the first stimulus check.
Then you are due the $600 for him for the second payment. There should be $600 on Line 30 of Form 1040. I am sorry for your loss. @pandother