In the same book Hermione booby trapped the parchment signed by members of Dumbledore's Army to leave anyone who betrayed their trust covered in boils - a deformation that may not be reversible - which is what happens to a friend of Cho Chang. And JK Rowling herself was actually surprised that some fans thought this unnecessarily and uncharacteristically cruel of the normally Adorkable Hermione. Keep in mind that she had been hit with a similar attack in the previous book.
She betrayed them to Umbridge- that was prone to give permanent scarring herself. The punishment she received was similar to the expected result of her betrayal- in other words, despite being cruel, the punishment was proportionate.
She betrayed them to Umbridge- that was prone to give permanent scarring herself. The punishment she received was similar to the expected result of her betrayal- in other words, despite being cruel, the punishment was proportionate.