Amelia Bird - Date of death

I assume Carol listed the year of death at 1867 and I am wondering what is the source of that information? Thomas Gasaway was my great-grandfather thru his subsequent marriage to Millie's sister, Mary Bird. I've never seen any info on the time and manner of death, nor where she is buried. I've always just figured it was between the birth of Millie's last child in 1865 and Mary's first in 1869--so before 1869 is as accurate as I can get. Just wondering how we got to the specific year of 1867. Carol? Or anyone else with info on the Birds?