If she's not eligible for a SSN, you can get her an ITIN to use as a tax ID number to file the return.
It's not clear which year you're talking about. One part implies a 2018 inheritance.
In any event, you can file jointly for 2018 (or file an amended return for 2017 to switch from married-filing-singly (MFS) to married-filing-jointly (MFJ) if you were married in/before 2017). If filing for 2017 amendment, you can use the amended return to ask for the refund you are due. If filing for 2018 next year, you can get that 6K as a credit on your taxes for 2018, which may result in a refund early next year.