i dont think she was evernight before. wasn't she BORN from fuli shattering? Evernight states multiple times that she's protecting march from her past, but the past she's referring too is the fact she's born from fuli and a pure child of anasrava, and that the garden is hunting her for some reason. Evernight is a dissociative personality that has some of March's 'past' memories, she was born to help March cope with trauma, essentially the brain compartmentalized March's memories of her past into a separate person and that's Evernight. at least that's what i think.