I can't recall how it started, all I can think of are these random blurs, events, and details, that combine and complement each other forcing a memory to be complete, when you gather a few of those blurred-out events you try to remember how old were you so you can put it in a timeline which how how old was she. Because you can't cope with the fact you went through that, you give your younger self her own body in which you don't live anymore.