"She's doing late-night research in the library where all of the useful books we've been reading are kept. And she's the Slayer. Slayers come with Watchers, who are members of an organization known for having a lot of useful books, among other less relevant characteristics; it follows that her Watcher is probably the librarian and very familiar with his useful books. If she asks him where to find the Gem of Amara, he'll be able to locate that information in his own library much faster than I can if it is there at all. That also goes for anything else we might like to look up."