When you go to the orientation/signup meeting on embarkation day, you will get a schedule. The schedule will have the activities planned, and their start time. You can review that schedule with your niece, and decide which activities she wants to attend, and which she doesn't.
Camp typically runs, for free, until 10pm. From 10pm to 3am, there is an extra charge (if you niece chooses to go).
Soda is an extra cost anywhere on the ship, and that includes Camp. If you buy your niece a "Bottomless Bubbles" sticker, that would entitle her to all the soda she can drink, one glass at a time.