As I said, it was a guy, you were wrong.
Transgender Person Speaks About Beating at McDonalds
http://www.freerepublic.com/focus/f-news/2709641/posts
http://baltimore.cbslocal.com/2011/04/23/mcdonalds-in-md-to-probe-response-to-beating/
Appears that way, looks like the girls were looking for a fight, according to this article.