Hermione had been lost in reading her book, she didn't even realise anyone was around her. So when someone tripped over her, she couldn't help but jump, instinct bringing her hand to her wand, pointing it in a direction that would be easy to defend herself. When she heard the woman apologise, she smiled, placing her wand down a little but didn't remove it from her grasp.
"Don't worry about it," she said, still shaking with the fright. "I shouldn't have just let you fall, I was too focused on my book."
She smiled apologetically up at the woman, reaching up to shake her hand. It was the right thing to do, after all.