Remember, as she revealed, she had never been slippered before and so had been totally unprepared for such a painful and distressing experience. A girl’s first slippering can be a particularly horrendous experience for her.
The teacher will have then told her: “Right, now go back to your place.” As she walked to her seat, every eye in the class would have been on her and she would have been fully conscious of that, and her red face would have become even redder. As she sat down, whether she had winced from the pain or been brave enough to suppress that wince, her anxiety will have been raised further still, and would have been noticeable.