Lily's honestly less interested in keeping a close eye on the fliers and more (and more) concerned with getting Harry settled down for his nap. Which is not the easiest of tasks with all these exciting things to watch. But Lily doesn't mind the distraction because she spends enough of her life worrying about these lunatics anyway. She's on hand, and has enough time when she's rocking and singing to Harry to absently watch things and think about what they're trying to achieve, what might be helpful, etc etc.
Eventually she gets Harry to sleep. The bassinet is covered and charmed with noise muffling, but still, you can expect to be glared at if you get too close and/or loud.