Hermione has her wand in her hand, of course- while she has been practising Hover Charms without it they require so much concentration that it's not at all practical to try it while she's concentrating on other things, such as locating promising-looking books.

She's surprised enough to be addressed that the volumes floating beside her take a sharp dip downwards, but a quick flick of her wand ensures that they bob right back up again and stay afloat- and then she gives the woman talking to her a polite but baffled look. "I'm sorry?" At which point her brain catches up with her mouth, and she glances towards the books. "Oh. You mean- well, every report I've heard describes the city as full of magic of some description." It sounds rather like an excuse.