There is something about this photograph that reminds me of "Scarlet O'Hara." I'm sure it must be the young woman's stylish hat, but it could just be her expression. While nowhere near as striking as Vivien Leigh, this young woman, identified only as "Lizzie" was still quite lovely. This CDV was probably taken between 1864 - 1869 so is indeed in the right time frame as Gone With the Wind.
The hat is a small boxy thing with a brim covered with what looks like little flowers and is secured under the chin with satiny ties. It covered with some type of lace and the right side appears to have something like a feather protruding up over the top. I tried to blow up the photo, but could not get a good view of these items. One other item to look at, she is wearing what appears to be a wedding ring and I have to wonder with the dark hat if she was not in the latter part of mourning.
The photographer was E. Cummings of Elgin, Illinois. I did not have much luck finding any information on Cummings although I did find an E. Cummings, photographers in the U.S. IRS Tax Assessment Lists on Ancestry.com who listed his address as Elgin and occupation as photographer in 1865. I also found an Edward A. Cummings of Elgin who enlisted in Company I, Illinois 127th Infantry Regiment on 5 Sep 1862 and mustered out 20 Jun 1865. His death was listed as 23 Aug 1922, Illinois death rolls. I suspect this is the same person.