Plus, there's the whole issue of what constitutes mental illness, and that legal debate. We barely know how to define mental illness in adults, much less in children. In a lot of cases with young people, so-called mental illness is just mental difference. It's nice that in your novel, Beckett's mental illness or lack thereof is left in question. She escapes with her fantasy life intact.
Fantasy is presented as a kind of freedom.
She's an extreme case, but I want her to be treated with respect. She deserves respect. Maybe it's a matter of nurturing young people so their difference doesn't turn into illness. And maybe that's where writers like us come in, to try to distinguish that difference and honor it. As adults who've been there and do remember.