On her return she should say NO she didn't get it because you did. She can get the 1400 based on 2021 and you don't have to pay it back. It is based on 2021.
What is on your 1040 line 30? Should be blank since you are only qualified for 2800 and you entered you got 2800. So that should be ok you didn't enter the 4200.
If you got a Stimulus payment for a dependent you aren't claiming for 2021 you don't have to pay it back. And they can get it on their own 2021 return. On their return they say NO they didn't get it - because you did.
The 3rd Stimulus payment is really based on 2021. The IRS just sent the checks out using 2020 to get them out fast.
See IRS Topic B first question
Questions and Answers about the Third Economic Impact Payment — Topic B: Eligibility and Calculation...
