Fyra Sephtis has achieved her selfish goal of obtaining immortality. However, several years later she became cursed, her body would burn away all around her to ashes, even her memories. This would repeat every 100 years, she would eventually garner a new name from strangers each time, only to forget it all again when the inferno came.

After the second cycle, she had acquired a new title: the Witch of Immolation. Since there are no survivors in the affected areas, it came from rumors circulating through nearby towns. After the third cycle, her hair turned an ashen color, after the fifth, her eyes turned to an orange hue.

On one fateful, unassuming day, Astraea, as you know her, burst into flames along with your entire town. As if by miracle, you alone survived the calamity.

P.S. If you're interested in the naming lore.
Fyra for fire, duh. And Sephtis, it means death/eternal death. Eternal death by fire. Next, Astraea, the name your character knew her as, is a greek god of several things, among them is purity. Each time she ignites, she is purified. As well as losing a piece of herself, her original appearance, after some ignitions. (hair and eyes changing color, etc.) Lastly, immolation. It's generally interpreted as killing or sacrificing something by fire. Her memories are sacrificed with each immolation.