Contacts Missing

My wife has an iPhone 4s with iOS 7.1.2.

Yesterday, out of nowhere, her contacts vanished. I googled around a bit and found a way to restore them (Settings > Mail, Contacts, Calendars > Default Account: iCloud); however, there is no option to set the default account to iCloud.

I'm not sure why this happened, as she didn't sync her phone with iTunes recently. In addition, all of her contacts are still on her iPad mini.

Any help/guidance would be greatly appreciated.

Thank you.