I've read the Gerstner and the Dodd biographies. Both have their idiosyncrasies—Gerster relays the family's history in an imaginative, almost novel-like setting, while Dodd sometimes offers slightly obnoxious psychological commentary—but I would recommend the latter if you had to choose, because she relies heavily on primary sources and manages to reveal quite enough of Sarah's character to stir up desires in the reader (when applicable

) to be more like that woman.
I thought
Feminine Appeal was really good, by the way.
P.S. That's Sarah Edwards in my avatar.