"Only she is listing sale on tax return"

The way one person gets the double-exclusion is for the other to Die:

"...allows a surviving spouse up to two (2) years from their spouse's date of death of to exclude up to $500,000 of gain from the sale of their primary residence."

So, they should undo the divorce, obviously. Then he must die (hey, I didn't state she had to be the one to make it happen). Then sell the house and still file jointly.