Duality by Becca Fogg

Jex thought she was an average, post-college girl—until she crippled a drunk and nearly incinerated a gas station. When her elemental powers manifest, she’s torn from her placid life and shoved into the war between good and evil. Forced to rely on new allies, including the sweetheart Captain of the Guards and her alphahole Valen, Jex must come to terms with her newfound ability before her enemies succeed in capturing her.