In 2004 it was thought that the last widow of a US Civil War veteran had died, then they found another one. When she died in 2008, it was thought that she was the last one. Then they found yet another one and she died in 2020. It's not impossible that there are still living widows who haven't been publicly identified.

The marriage took place in 1936. The last known veteran didn't die until 20 years later. In many states it was (and still is) legal for 13 year old girls to marry as long as they have parental permission.

It's possible (albeit unlikely) that there is a widow who won't celebrate her 100th birthday for another decade or two.