Is Esther Herring's LNAB really Marion?

Question

I've seen two books (see profile) stating that Esther Herring (the wife of William) of South Carolina was a sister of Gen. Francis Marion.  Do any South Carolina experts have resources that would confirm or deny the relationship to the Marion family?  Her 1812 will doesn't help and I can't find any helpful marriage records.  

Comments

Not relevant, but I think after George Washington [your-favorite-surname-here], I see Francis Marion [your-favorite-surname-here] more commonly than any other forename/middlename combination. People really loved the Swamp Fox, and I hadn’t heard of him until I got way into genealogy.