@schulaw1  "The IRS has already told her that because it was sent to him she's not eligible to get the stimulus payment."

The IRS is not like that monolith in Utah, but one poorly-trained phone clerk can also be replaced and removed.  Try the HUCA method (Hang Up, Call Again).  Better yet, the Taxpayer Advocate.  There is no reason your client's superseding MFS return can't be accepted, and no reason the EIP can't be claimed on her 2020 return.  The only thing necessary for the triumph of evil is that good people do nothing.