I think more clarification is needed.
Injured spouse form 8379 is used when you are married filing a joint return, and your refund is being offset for your spouse's past debt from before the marriage.
Innocent spouse form 8857 is used when you are being held responsible for a debt due to a joint tax return, where you argue that even though you signed a joint return, you did not know about the errors because your spouse hid them from you.
https://www.irs.gov/individuals/innocent-spouse-relief
If this is a debt due to a joint return that was adjusted by the IRS, your spouse has since died and you are still being collected for the error from the joint return, that is a case for innocent spouse, not injured spouse. If you are remarried and your new spouse is being held responsible for your old debt, your new spouse can file for injured spouse relief.
Innocent spouse generally must be filed within 2 years of the notice of deficiency, so you may be too late. But you can use the same form to ask for equitable relief or separation of liability, which might reduce what you owe to what you already paid.
