Scion of the Fox The Realms of Ancient, Book 1

Roan Harken considers herself a typical high school student (well, maybe not so typical) but she's uncovering the depth of the secrets her family left behind. Saved from the grasp of Death itself by a powerful fox spirit named Sil, Roan must harness mysterious ancient power... and quickly. A snake-monster lies in wait, hungry for the sacrifice of spirit-blood in exchange for keeping the flood waters at bay. Thrust onto an ancient battlefield, Roan soon realises that to maintain the balance of the world, she will have to sacrifice more than her life in order to take her place as Scion of the Fox.