Not enough information to comment one way or the other....
What was said? How functioning was the child? Where did the girl learn the potential string of profanity? Do you value having a classroom subjected to one student getting their way in cursing?
Children with DS, especially a teenager, impulsiveness is another common challenging behavior in children with Down syndrome as they may act without thinking, which can lead to behavior issues and difficulties in social interactions. In many cases they also suffer from ADHD as well. This was an act of cruelty to a young woman who does not have the ability to truly know right from wrong yet. This should overcome your 4 obnoxious questions.