maggie10,
The eligibility requirements for the 2021 recovery rebate credit are listed at
https://www.irs.gov/newsroom/2021-recovery-rebate-credit-topic-c-eligibility-for-claiming-a-recovery...
In particular, if your oldest could be claimed as your dependent on your 2021 taxes, even if you didn't, she isn't eligible.
If that is not the case, she likely failed to claim it on her return. She should wait a few weeks and then prepare an amended return claiming it. The 1040-X form is very easy to fill in by hand with her original return in hand.
