The flag commonly refered to as the confederate flag, was actually a battle flag that was used to identify Confederate troops on the battlefield.
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actual Confederate flag looked to similar to the US flag, causing much confusion in the the early stages of the American Civil War.
The war had less to do with slavery, at the time, as relatively few southerners actually owned slaves. Slaves were an expensive commodity. The war began over the issue of states sovereign rights, then evolved into an issue over slavery when President Abraham Lincoln issued the Emancipation Proclomation, freeing slaves only in those states in open rebellion to the US.(border states, loyal to neither, were left alone). This issue effectively kept England from formally recognizing the Confederate States as a nation, severely limiting their chances for winning the war. Which, of course, they did not.
The image of the confederate battle flag has since been adopted as a symbol used by various white supremacist groups, most notably the KKK, and the Aryan Nation. This fact, coupled with revisionist history of the Civil War, has turned a once proud symbol into a feared, and much maligned, emblom of hatred.
This has been your Bill O'Rights history lesson, for the day. By the way, I am a Civil War Re-enactor, and have portrayed soldiers, and officers, from both sides of the conflict. Hope this helps?
Oh, and by the way, the kid knew better. Kick her in the butt, and tell her to get on with her life.