Oddly enough, she is buried in the Agee or Hasty Cemetery near Hasty, Newton County, Arkansas.
I cannot find anyone else that she is related to buried in the cemetery, and it is well documented that she and her husband lived in the Bellefonte area of Boone County most of their adult lives.
Turnbo quotes William Eoff who places them among the "early residents on the left hand prong of Crooked Creek in Boone County Arkansas". A biography of her husband Robert Capps notes "Mr. Capps has been a resident of the section in which he now lives for nearly sixty years, has always tilled the soil, and besides the farm of fifty acres on which he resides, he is the owner of other valuable lands in Newton and Boone Counties." Possibly she died at another farm they owned and was buried near it.
In any case, it seems like it requires some explanation, but also certainly explains why no one could find her tombstone! It was rather far afield...