When she ordered Aberforth Dumbledore to stun her and make it look real, Hermione didn't expect to end up in an uncomfortable bed in St. Mungo's Hospital for Magical Maladies and Injuries. Apparently, there was just a hint of hostility towards her that the elder wizard still felt. She couldn't blame him for being so aggressive when given the perfect opportunity. After all, a stunner was exactly how the entire mess began months earlier. What he had to endure living in one of those tiny cells in Level Eleven for so long couldn't have been easy. Maybe it was cathartic for him to use more force than was absolutely necessary.