The girl needed to be restrained pure and simple as soon as she became destructive. The thing I don't get is that it appears in the video that by the time the cop got there, she had already calmed down, and was sitting quietly in a chair.
I would have supported some type of restraint, including handcuffing when she was being destructive, but once she calmed down -- as she appeared to do -- I think they were out of line to hand-cuff her.
Maybe she saw the Law thru the office window and knew exactly what to do.