Seek and you will find

Astoria outlived history. Her immortal life is both her curse and her gift. No plague, gunshot, stab wound, or anything can kill her. Her eternal life is her greatest torment. Three centuries of life had rendered her too tired to live, and set off to the 21st century to find what will restart her clock, and grant her the rest she needed. It turns out, she will find more than what she asked for.