"and said they answered all the questions correctly"

Not living on $4k, they didn't. They likely overlooked "could be claimed by someone else."

If the person is not a dependent in 2020, then they would be entitled to the payment/credit as individual filers. That doesn't mean "not being claimed." It means "no longer qualifies as a dependent."

Your client likely thinks filing for herself = no longer dependent. Let's not let the real world get in the way of wishful thinking.

If you still want to help them, send them to the Interactive wizards portal for determining dependency:

https://www.irs.gov/help/ita

And:

https://www.irs.gov/newsroom/economic-impact-payment-information-center-topic-a-eip-eligibility

https://www.irs.gov/coronavirus/second-eip-faqs#Eligibility

One for each EIP.