Hermione didn't see why she couldn't. As long as she was able to get one of his possessions, it should work. Draco made her swear a vow that she would never tell anyone the spell he taught her. Now that the world was different and the Dark Lord was dead, she didn't understand why it was such a big deal to him that his spell remain a secret, but she wasn't one to break vows when they were made. Unless they were of the marital kind. Those she'd broken more often than she kept them.