I was gonna post this story, but I guess you beat me to it.
I've seen kids freak the hell out and the can do more than you think. School desks aren't particularly heavy, and you don't need to be able to lift a heavy bookshelf to tip it over on someone(think of people who tip vending machines).
That said, it sound like it's extreme, but at the same time I'm not sure what else one would do. It sounds like there were a few people there trying to calm her down and it wasn't working.
I remember one time in 7th grade when a mentally retarded girl who was in my "do homework or something" class freaked out(not the first time she did by any means). She ran up and down the halls screaming and at one point shouting, "STOP CHASING ME! I'LL JUMP OUT THE WINDOW(we were on the 2nd story)! DON'T CALL THE COPS!" She also threw chairs around the classroom, flipped a table and ran down the hall banging on the walls. The teacher, a couple of other kids in the class, and me tried to calm her down and eventually succeeded. Later that day when I was talking to a friend who had a class down the hall when this happened when he asked me if I knew what on earth that noise was that morning. I told him, "oh it's just Marcee having a freak out again". Did I mention this girl had a beard? (To be clear I'm not trying to make fun of retarded kids or anything.)