I agree. I think it's way too much for an honest mistake. Now, if the kid was purposely acting up and taunting her, then it would be more appropriate.
I remember once when I was in the 6th grade, the teacher had a very strict rule about no talking during lessons. I hadn't heard something he said and asked the student next to me what it was (in a whisper). He had me stand up and say what we were talking about. I told him, and the other student corobberated it. And he still said that because I broke his rule (I should have raised my hand and asked him to repeat it, he said), the whole class would miss recess that day. I was already unpopular enough, and that didn't help matters. They gave me crap about it for weeks afterwards.
On the other hand, I remember this classmate in the 9th grade who was always willfully being a goofball in my Algebra class. That teacher had a strict rule about cracking gum and blowing bubbles with it during lessons. She sat in the desk right in front of his and blew this huge bubble right in his face one day. He asked her if she had forgotten about his rule, and she goes, "No." So he made her stand up in front of the room with her wadded up bubble gum on the end of her nose for the rest of the class. A bit much. But I'll tell you what - she never blew a bubble in his face again.