I can't answer the question about where specifically Frederick Propst's widow was buried. However, I can tell you that her maiden name was most likely NOT Swadley, as has been traditionally reported. Instead, she was very likely the daughter of Valentine and Maria Catherine (Oberlin) Pence. I have written an article discussing all of the evidence regarding this, that was published in "Allegheny Regional Ancestors," Vol. 7, #3 (Fall 1998). You can order this single back issue for $5 by writing: ARFHS, PO Box 1804, Elkins, WV 26241.
It is likely that descendants guessed that Barbara had been a Swadley, because Henry Swadley WAS Frederick Propst's brother-in-law; they had married Pence sisters, Mary and Barbara, respectively. I will add that part of what confuses the matter of where Barbara is buried is the fact that she remarried to Jacob Conrad Jr. in 1808. It is actually likely that Barbara ((Pence)Propst) Conrad died between 1810 and 1820, as she is not listed in the Census with Jacob Conrad "Sr." in 1820, and he did not name her in his will written in 1824. So, the question is, "Which husband was she buried with?"