The date she sold the house after her husband died, it was only her house, she was alive and indeed a widower.  12/31/24 She was not alive.  I guess that depends on interpretation.

Husband never owed the house at all.  Sorry, should have clarified.  No step up.

Widows elects Married Filing Jointly.  There's no box for Widower.

For the year someone dies, you just write DECEASED and the return has an executor or personal representative sign it.  

I guess I can leave 16 blank but it seems she is a widower when the house is sold.