Your other accounts on the web say Sarah O'Neill married Casper Hardy, son of Joseph Arnold Hardy and Julia Anna (nee Gardner) Hardy. This says she married a Willie Hardy. Are you getting it mixed up with Sarah and Casper's son's name - William C. "Willie" Hardy?
I know this Casper Hardy also fought in the Civil War.
I also was wondering, due to the time frame, if these O'Neills are related to the writer Eugene O'Neill?