She was from Mansfield. Texas, a town of very dubious pedigree in terms of race relations.
And yet. Ella Mae Morse not only sold well to African-American audiences, she was, apparently, thought to actually BE African-American by many who had not seen her picture.
AFAIK, there's no story about how she absorbed that feel so young. Mansfield was (and might still be for some) a Klan town. So this little white girl was getting something somewhere to sing like that, so totally unaffected.
Maybe she got out of Mansfield and moved up to Dallas. But even then, a young white girl would not have unlimited access to all the cultural opportunities that were available...
Sam Phillips was wanting a White boy who (supposedly) sang black. And Wanda Jackson gave Capitol a teenage wildcat/sex kitten. Exploitation. Business. Distraction and distortion.
Ella Mae Morse was to one degree or another all of that, minus the hype. She was natural.
Now, is it just me, or does that sound like Rex Middleton's Hi-Fi's joining in on "Rock Me All Night Long"?