Do you have your paternal gr-grandmother's married name if it is different from your own? I find Ella Marie Abernathy with parents Lon & Ida Bell and at least 2 older sisters on Paducah census records (1920 & 1930). Unfortunately, while the Soc Sec Index has 424 Ella M. [somename] in their Soc Sec Death index born either 1917 or 1918, it appears that one might need to know her married name to find her, since there are so many possibilities.
And can you narrow down the year and probable location of death? Did she live nearly all her life in KY or did she, her husband and/or a family member (with whom she may have been living at the time of her death) move out-of-state? If so, where to? If you have some of that information, you should be able to get a copy of her death certificate and perhaps even a birth certificate. And you'd probably want to look for the death certificats for her parents, as well. Since Lon & Ida were farmers and probably died before Soc Sec Numbers became manditory for everyone, they may not be in the gov't's SSDI records, but knowing the state and probable county in which they died might enable you to find their death certificates.