Since she can remember, she's been dreaming of another life.
She wrote her other name down once, and then, on consideration, burned it.
The dreams come in no particular order, not even following any plot. They don't confine themselves to ages she's already experienced. She keeps a coded dream journal, putting down indirect ciphered reminders. Her dream self is emphatic enough about magic being unsafe to try if you don't know what you're doing that she never in fact tries it, but she greedily collects tidbits of information on how rituals work and what they can do. Her paranoia about recording any of it in any remotely readable form is partly out of generalized caution, and partly because the penalties for masquerade-breaking in magical society seem, from her waking perspective, uncomfortably harsh. Safer to just never let on to anyone that any of this is happening.
She occasionally, very carefully, looks up information from her dreams. The town her dream self lives in does not exist, and neither does the bigger town nearby—but the lakes they were attached to do both exist, and her waking self has never been to either, never even seen them on a map before she ventured onto the internet in search of them. None of the companies or websites directly connected to magic in her dream life seem to exist in any recognizable form in the waking world. Her dream self never remembers her waking life at all, nor thinks of herself as dreaming. She confines all speculation about the metaphysics of this situation to indirect statements in coded journals. The really indisputable evidence turns out to be, of all things, math homework: she wakes up one day from the middle of a calculus problem set, and looks up what calculus consists of, and concludes that she cannot possibly have reinvented that in her sleep. Then the same thing happens again a month later with trigonometry. And several more times with literature, on the rare occasion when she dreams about a book she hasn't already read while awake.
Her dream self has a family. Two sisters, two parents, an aunt and some cousins, a grandmother. None of them particularly resemble anyone her waking self has met. She tries not to let the comparison colour her impressions of her actual family, but it's hard to avoid. Her family is... fine? Normal? But the rules and expectations and exertion of authority can feel stifling next to her dream family's automatic camaraderie. She at least succeeds in never uttering the words "you're not my real mom", and tries not to think them too often, either.
In her random scatter of dream memories she is never older than sixteen: she's been a baby, a toddler, a child, a tween, a teen, but never graduated high school, never gone to college. This leaves her a little superstitious about her seventeenth birthday, so she arranges to spend it by herself, in case of unforeseen events. The day begins bright and early with a walk in the park, rays of sunrise shining golden through the fog between the trees. She admires the beauty of nature and tries to remember last night's dream, which she thinks was about learning a spell for washing her hair really well.