Interesting that in Cox, five of the six versions with enough words to identify the weapon specify a knife and one only one mentions beheading. Although put together, as Joe suggests, "The Jealous Lover" (and other titles inc. Blue-eyed Ella) existed independently of "Pearl Bryan." Jackson, Willie, etc. killed because of jealousy. This song seems to be based on "The Murder of Betsy Smith," a 19th c. British ballad.

As the story about Pearl Bryan spread, beheading crept into the song and the name changed from Betsy, Ella, Florilla, Nellie, Nola, Edna, etc. to Pearl. The singers either did not know the whole story of Pearl Bryan, or did not want to put abortion in the song, but they did, at least, use her name. Closely related versions in Cox ("Folk-Songs of the South," pp. 197-202) show the change in the last verse-

"The birds sang in the morning, but mournful was their song;
A stranger found her body [Ella] in a cold and lifeless form."

"White flowers growing about her, close by a grassy mound
A stranger found Pearl Bryan, cold, lifeless, on the ground."

And finally,
"While farmers plowing o'er her, shrill was the tempest sound;
A stranger found poor Pearl, cold, headless, on the ground."

Randolph collected only "The Jealous Lover" in the Ozarks.
He says Barry (1909 considered the song a native American ballad, but later pointed out its relation to "The Murder of Betsy Smith,"
published in England early in the 19th c.

I will post "The Murder of Betsy Smith" in the "Jealous Lover" thread 73375: Jealous Lover .