We have written about women fighting in the American Civil War. In fact I wrote this article on this blog about 8 years ago.
Here it is.
https://civilianmilitaryintelligencegroup.com/4564/women-as-soldiers-in-the-civil-war
Here are some more solid examples of the eight women who dressed in drag and fought at Antietam.
Union cavalryman Jack Williams (left) fought in 18 battles and was
wounded three times and taken prisoner once.
He was later revealed to be Frances Clalin a mother-of-three from Illinois

Sarah Edmonds served for two years in Company F of the second Michigan Infantry.
She later wrote of her experiences in her memoir Nurse and Spy
Dual identities: Irish immigrant Jennie Hodgers enlisted in the Union army
as Albert Cashier and then remained a man once the war ended
Sources:
They Fought Like Demons: Women Soldiers in the American Civil War; DeAnne Blanton, Lauren M. Cook; 2002
Woman of Valor: Clara Barton and the Civil War; Stephen B. Oates; 1995
A Savage Thunder: Antietam and the Bloody Road to Freedom, Jim Murphy; 2009