EndBringer by Andrew Phoenix

Lief Tahi is a vengeful sixteen year old out for the blood of her mothers murderers. With the supernatural power of a tank behind her fists, not much stands in her way. With her witch brother Reve and Eternal artifice wielding brother Kei, Lief fights in the dark alleyways of mankind where shadows and wicked things play. Gods fall, cults rise, and things slither in the dark that hunger for the destruction of the Earth. Lief must make the decision to let her lust for vengeance go or take up arms against the coming blood tide.