Deposited wrong stimulus check into my account, what happens now?

Yesterday 23, April  2020

I unknowingly took my girlfriend's stimulus check as live together and had the checks sitting together. I signed my name and put my account # and deposited her check through my ATM, which supprisingly didn't notice the name on the check didn't match the endorsed name. 

  We didn't realize this till today when we went to deposit what we thought was hers and the teller at the drive up said the name on the check doesn't match her accoun since its my check.  I called my bank and they said the check had already posted and there was nothing she could do. She said the error might be noticed and sent back to me, but if not what happens?     I worked at a bank processing center 25 years ago and remeber that there were checks that would be rejected from the scanning machine and had to checked by hand. Do banks still do this? What happens now? Big pain in the ***.