The nature of Klaus Wulfenbach is one of curiosity and analysis. As such, he appears to require his captains to take logs in an organized fashion. Bang is no exception, as found when Klaus discusses with her she had seen since her last report. Interestingly, the spine of the book reads Phenomena Observed: DuPree. How he convinces Dupree to take time away from her busy schedule of killing, maiming, and torturing others is a mystery. Perhaps he simply suggested she needs to record all of her despicable acts for posterity, so she will be known infamously forever.
Most likely she simply delegates the task. We can see one of her