"Hey Maddy, I have a confession to make." You say as she throws the soiled rag into her bathtub and washes her hands.
"What?" She looks at you, visibly pissed. "...and why are you smiling like that?"
"I ammmmm," you say coyly, leaning against the wall and making a snarky shrug, "a mind-controller."
"...what?" She turns off the water and gives you an intense look.
"Heh. Okay, basically, I have the power to control anyone's mind, as much as I want. I'll prove it." You stand straight and cross your arms. "I'm going to make you pick your nose. Try with all your will to NOT pick your nose, okay?"
Madison shakes her hands into the sink and heads for her bed.
"You're so stupid." She declares.
~Pick your nose~
"Lucky chance!" She retorts, right index finger firmly planted in her right nostril. "I just so happened to WANT to pick my nose at that exact moment!"
"Well of course that's what you THINK." You say smugly, leaning against the wall outside the bathroom. "From what I've seen, the mind-control effects leave no footprint on the person's psyche."
She's getting comfortable on the bed, adjusting to the feeling of the diaper, and defiantly opening her laptop in ignoring you.
You watch her for a moment, and say...
~Take one of the diapers from your dresser and throw it out your window~
You witness her do exactly this, and then get comfortable behind her laptop again.
"Hey Maddie, why did you do that?"
"...throw the thing out of my window?" She mumbles.
"Yeah that. Why did you do that?" You lean against the bed beside her.
"I dunno. I hate these stupid things and my family is stupid for making me wear them." She scoots herself away from you a bit. "And you're stupid for seeing me naked."
Her behavior is interesting in itself; you specifically made her 'totally fine and happy' with your being here. This must mean that she is happy with your general presence in the house, but that she could still get mad at you over certain individual things at different times. This was already shown a few moments ago when the mother handed you the diapers, but this was a much more clear-cut and definitive example.
"Why would throwing one of them out the window help you in any way? Won't you just have to go get it at some point?"
"I don't know! Shut up!"
"Don't you realize...it was something you were MADE to do, by me? That's the only possible explanation."
She completely ignores you, not seeming to believe you at all.
Guess you'll have to come up with a convincing piece of evidence.