This unidentifed young woman may well be a vivandiere, one of those unoffical women who were accepted by and often accompanied their regiment. These were not women who disguised themselves as male and enlisted, nor were they cheap "women of the town" but were instead women who played a ceremonial role in military parades and frequently also performed the duties as a nurse, sutler or other function. While most remained behind when their regiment left their home state, a few followed the men into the war zone.
Note this woman's full military size drum, the canteen on her hip and her very basic military style uniform adapted to female style and compare to this other picture of a Daughter of the Regiment.
Photo by Smith & Richardson, Birmingham, Connecticut.
Taken c. 1863 (+/- 1 year)