Taking Angels, book 1 of The Angel Crusades

Britt Anderson went along with everything the doctors said for nearly four years, but she was still dying at eighteen. The cancer had won leaving her without a future, without any options, and without control. No control, except for how she would leave this world. As Britt tries to end her life by going into the frigid waters she realizes her mistake. She struggles to get back to shore, to cry out for help, but her atrophied muscles are useless and the frigid water steals the breath from her chemo-scarred lungs. Despite her father's attempts to reach her, she flies over the waterfall. When Allister Parks finds Britt's fragile body on the riverbank something calls out to him. Ignoring the warnings of his sister, Allister brings Britt back from the edge of death. The only problem is that an Eternal like Allister isn't allowed to touch those who have already passed from this world. It is forbidden; an infraction punishable by death. As Britt relishes her new cancer-free life and senior year of high school, her very existence threatens Allister's place in this world. Allister struggles to keep Britt a secret from the Eternal Council and out of the hands of the only Eternal who already knows the truth: the one who stole her guardian angel.