The Coal Elf - The Coal Elf Chronicles, #1

Santa is real, but this isn't your childhood Christmas tale!Ember Skye is a fed-up teenaged Coal Elf with a big ashy chip on her shoulder. Torn away from her carefree life Aboveground, she was forced into a world of dirt and darkness in the Mines. Now, the coal is starting to take its toll. Plus, being the only girl-elf coal miner at the North Pole is not fun at all!Then there's--a power-hungry, twisted elf with a serious grudge against Ember.
Hellbent on overthrowing the hierarchy, he leaves the smoking gun in Ember's lap: the Naughty List. When a mysterious illness threatens to decimate elves both Above- and Underground, Ember is thrust into a journey that will see her confront the demons of her past and lead her straight to the head of the North Pole himself.