IPhone won't find any Wi-Fi networks?

Ny mom just got an iPhone 4, I got the iPhone 5. I connected to our home Wi-Fi but when I try to connect my moms phone it won't show any networks available? It shows up for me and not for her.

There must be a fault with the iPhone 4.

Try resetting it by going to Settings > General > Reset > "Reset All Content and Settings"

If that doesn't fix it, you'll have to take it to an Apple Store and get them to have a look at it.