She sense waves of dark magic, of course, from the assembled Death Eaters and Nagini, and Voldemort himself, but she can’t distinguish anything specific to a Horcrux. Draco has held both the cup and diadem in his hands, though, so he has a better understanding of what a Horcrux feels like. He’s still looking around as Neville steps forward in what is surely a suicidal move. Theo and Blaise are holding on to Pansy, who is doubled over, sobbing.