It doesn't matter whose SSN is on the form, if the money was paid to her after his death.  Is this the remaining amount in an IRA, by any chance?  How much was it, anyway?  Enough that if it's taxable to him, she can't claim him as a dependent?  

If the money didn't go to him before his death, you don't need to file a return for him.  Don't be OCD about IRS matching it up with his nonfiling status and sending a CP 2501 next year.  They might not even be around then, and was it really more than $20,000, to generate enough tax to worry about?