Topic: I really need your help guys.

Is your Wii U connected to the internet and is New Super Mario Bros U. up to date? Pro Controller support was added in an update.

How do I connect the Wii to the internet?

You would use wi-Fi out of the box - set up via the System Settings app (channel icon has a spanner on it). Otherwise you can get a Wii USB-Ethernet adapter.

The gamepad's nearly as big as the actual console. Are you sure she didn't give you a wii and tell you it's a wii U?

@Dezzy He managed to connect a Wii U Pro Controller (complete with the player lights on the bottom) on the main menu, so it's got to be a Wii U.

If you took a picture of the main menu we could settle the question of whether it's a Wii or a Wii U.

EDIT: Nevermind, @Bearclaus had a better way to tell

When NSMBU released, there was no pro controller support. The reason your pro controller is turning off is because the game needs to be updated. I would also recommend updating your system as well since that will add Wiimote and Pro controller support for both the eShop (I think) and definitely Miiverse. The only thing you will not be able to do without a gamepad is access system settings. Yes that does suck but, you can still play and enjoy the system without ever going into system settings.

Launch the eShop. It should trigger a system update. After that, start the game- it should trigger an update which will patch in pro controller support. Close the game out, go to the blue downloads box on your home menu, and see if the update is downloading. After that you're all good. In the meantime though you can always use a sideways Wiimote

Don't you need the Gamepad to access the online and update functions on Wii U? I think he needs to borrow a Gamepad from someone to make it work.

True, he's not joining an online network. Possibly there's a system update included with newer disc releases like the Wii used to do? Really it's better to just call Nintendo and see about getting a replacement Gamepad.