Then think I shall lean on European folklore and make a changeling. More specifically human child who spends time amongst fey/spirts. Something that happened before she could remember and brief enough (at last from outside perfective) to not seem like anything too unnatural.

As I think about it more. Perhaps I clean into the Slavic side. It might be quite fun to combine modern ideas of gender and the association of intersex people with magic in Slavic culture. Unfortunately that's a bit of a tricky topic when it comes to such changeling as historically "changeling" was able given to kids nowadays we would likely consider autistic. Of course, it's not a one-to-one translation, but it might inform some aspects of said character. Should I do that, I would rather avoid exact recreation of my experiences, but at the same time I don't want to fall into stereotypes.