Is there agreement on who is claiming the child in 2020?
If you claim your daughter in 2020, the reconciliation of the stimulus will cause you to collect $500 on Line 30. There is no need to amend 2019 tax return to make this happen. The payments in the spring was an advance against taxes owed in 2020 and the 2019 tax returns were used to figure out how much to send to everyone. But sitting here in late 2020, nothing about the 2019 tax return matters with respect to the first stimulus payment.
Mother's stimulus tax reconciliation on her tax return will say she received too much. (because the daughter is not on the 2020 return), but by law is not obligated to return the excess money.
That means that one child could cause two $500 payments to be made because of the way the CARES ACT and the IRS is administering this thing.
The same thing is going to occur with the 2nd stimulus payment because the payment will be based on 2019 data, but the reconciliation is based on the 2020 tax return with no obligation to return over payments.
