It seems to me that the form this trauma she barely remembers despite its devastating impact on her life took the form of a devastating impact on her face. Somehow or other, some random object (possibly a ball from a pick-up game the neighbourhood kids were playing) got away from its owners and smashed into Elly while she was simply going about her business. This seems to be the way of it; stitches might come out, swelling might go down but her self-image seems to have never healed from this thing that she only vaguely remembers.
She also doesn't remember why she craves isolation so badly. I have an idea about that which also explains the paranoid dread that she isn't allowed to talk ever and has to meekly agree that her opinion is something she 'knows' to be a lie. If I'm right, its source is the botched attempt at first aid to a frightened, angry child and a hatred of the 'false' compassion of people who lie about her looks. More on that tomorrow.