Hermione's hands practically itched to take the other wand, but she knew that it wasn't hers - she'd watched them break hers, and so she kept herself close to Harry's side and let Ron grab his instead.
Why would the Death Eater bring Harry his wand unless he was - "You're letting us out." She said succinctly, putting it out loud for the boys. She didn't know why, but she also knew that there wasn't enough time to ask right now, and she prodded Harry in the side and nodded for him to go up the sodding stairs.