Possibly Yasuyo & Don did not have children, and Don pre-deceased Yasuyo?
I live near a major military installation. It is possible that this lady was born in Asia & came to the US when she married a military man. If his VA benefits were covering her stay in the 'care home,' the VA should have contact information for next-of-kin.
Provided family survived her, of course.
I suggest contacting the church, email is likely available.
Church secretaries Know Things.
We do not sleuth family members, but in some situations find needed information this way. I Googled Don SMith, Marhsalltown IA obituary.
I did not find a wife named Yasuyo, but my eyes are tired from reading...and there are still possibilities.
At a genealogy site I use frequently, there is also a Yasuyo Grimmius listed in Marshalltown, Iowa, with a slightly different birth date.
The site includes naturalization records -- with both the petition & the certificate viewable. At the time of her petition for naturalization, her husband was a Gene Thomas, and they were married in Tokyo. She entered the USA in July of 1957, and became a citizen on May 1, 1962.
No luck using Yasuyo Thomas -- so I have to wonder what happened, there, ya' know?
Grimmius does not seem to be a Japanese surname, either. Numerous people with that surname in Iowa, but none an obvious candidate for her family.
Confused, indeed.
Please let us know if/how the church responds.
(Won't bore you with my person Church Secretaries Know Things tale.)