As i said before, childhood belong to a CHILD, she's NOT a child anymore, there's no childhood for her anymore. And why turn back to a teen make she feel guilty, she already feel guilty now, even if she not taking APTX, she'll eventually grow up and become teen again. No matter what happens, Ai Haibara is Shiho Miyano, you can't deny yourself, instead of running away from yourself, live with it, change it the way you want. She has to get back to her true self, and become Shiho Miyano that she wants: A normal girl just like others with no BO, no ATPX.