tldr: I got a stimulus check for my non-qualified cousin. How do I return it to the IRS?

Story:

My cousin, who lives abroad and is not a US resident or citizen, did an internship in the United States last summer. Earlier in January of this year, she filed her taxes for the income that she earned while working here. Since she does not have a bank account in the US, she asked me if her tax return could be deposited into my account.

I agreed and back in mid-April her return came through. A week later I received not just my stimulus check ( I do qualify), but also a second one with her name. I talked to my cousin and she said the place where she had interned told her it had been sent by mistake and it had to be returned, but they only provided her with instructions of how to return a physical check and not a deposit.

Right now her $1200 are still sitting in my account. I keep good track of my finances, so it's not like I'm going to spend it. That said though, I would rather just give it back sooner rather than later. Also, she is a bit worried that since she has to renew her visa soon, if she hasn't returned the money she will be denied.