Wouldn't put it past her, personally.

6026055
Play Bioshock and you will.

I think it was because she was using manipulation and intimidation to her advantage, because she knew how sensitive and awkward Twilight was. She used that strategy to break Twilight and to make her give in. That's my theory anyway.

(P.S. Principal Cinch really creeps me out, I don't like her at all.)