Hey JD,
I know you are asking Corey, but I thought I might take a shot at an answer. This song has always baffled me too. Check out Stephen Calt's 2009 book Barrelhouse Words: A Blues Dialect Dictionary. I'm not totally convinced by his definition of a kind-hearted woman (p. 143) as "a woman who caters to a gigolo in exchange for sexual fidelity," but I think it's in the ballpark. Calt does also include lyrics quoted from Lucille Bogan's "Kind Stella Blues" and Charley Patton's "It Won't Be Long" as well as Robert Johnson's "Kind-Hearted Woman," though I can't say I see a single, unambiguous use of the word kind between the three songs.
I'm guessing that kind-hearted is an idiom that means something like solicitous or ingratiating, also implying that someone is manipulative. Also, in all three songs - Bogan's included - the word is used to describe particular women in a way that is unflattering and, according to more contemporary moral values, sexist. There is nothing in the Oxford English Dictionary which suggests that the word kind in standard English can be used in this manner, but I think with this idiom it's an ironic use of the word, much like referring to something as bad when you mean really good, cool, or, as we say in Massachusetts, wicked awesome.
Anyway, I just thought I would have a go at an answer.... An answer, not THE answer, mind you.