You wait until her sobbing has died down, for the moment at which she desperately looks back up at you. You shake your head.
"No." You tell her straightly. "I'm not changing my mind."
Her eyes are filled with despair. She stands up, looking confused and distraught, on top of very uncomfortable by the mess in her diaper.
"Alright Maddie," you get up and take her hand, "it's time to get you changed."
She strikes a defiant look back at you.
"...Maddie," you chuckle, "trying to defy me is not going to go down well."
Your words strike her with fear, but not as much as you were thinking they would. You can see she's trying to make you her enemy, but she can't quite; not with your 'be okay with me being around' command in effect. You imagine she's actively *trying* to override her approval of you, but there's nothing she can do about it.
A product of the Mind-control Sapphire, as operated by you: Madison is trapped in a psychological contradiction. She kinda enjoys *you*, but hates everything about you and what you've done to her and her family. At least with someone you hate, you can at least choose to hate them--openly or secretly. But with Madison's relationship with you...she isn't able to come to the conclusion she thinks she should. The confusion brought on by this, in fact, starts to calm her down.
Her muscles relax. You feel the loosening of her wrist-muscles in your hand, so you let go of it.
"So um..." She bites her lip, her hatred subsiding (to her baffling disbelief, but gradual acceptance). "Why did you do this to me?" She asks, looking up at you. "This is really gross and weird."
You smirk. "Let's get you cleaned up." You put a hand on her shoulder.
A few moments of coaxing her go by before you have her lain down on her floor, legs spread as you untape her diaper. Her crying comes back again as you open it up and begin wiping her with towels, but it's at least silent sobbing this time.
"I don't know why." You finally answer her question. "I just think a girl wearing diapers is really cute."
Madison has no reply, only more tears.
"I mean," you continue, "I've babysat a few times, and while I love how cool babies are, it sucks that I can't talk to them, you know? I enjoy taking care of things that are helpless, but I also like caring for something that I can have an interesting conversation with."
You conclude the cleaning, and place a fresh diaper under Madison.
"So when I got my..." you were about to tell of your Sapphire, but you realized it'd be better to not let her know of the source of your power (tucked in your shirt) for now, "...ability to control minds, one of the first things I thought of was taking a kid who seemed interesting or fun, and making her helpless like a baby."
By the time you tape her in, Madison's tears had run out.