About the movie "Ｃｈｉｃａｇｏ"

In the latter half of this movie, after Roxy was judged innocent, one woman shot one man and then she was arrested in front of the courthouse.

It was the sudden incident to me, therefore I do not understand why she killed him.

Is there anyone who knows the reason?

About the dance party in the movie `Little Women`.

As I was watching the movie `Little Women` in the class, I noticed few soldiers were in the dance party with other gentlemen and ladies. I thought that only high-society people could attend that kind of dance party, but the soldiers were not even a commissioned officer, they were sergeant and corporal according to their chevron on sleeve. So now, my question is that were anyone allowed to join that kind of party or not.