You walk up to Emily and grab her by the wrists.
~You are aware of my presence again.~ You command.
She jumps and yells a little from the surprise of you suddenly constraining her.
"ACK, what are you doing?" She exclaims.
"Emily, you fancy yourself to be pretty smart, don't you?" You ask.
"....yeah?" She answers, pretty scared.
"You think you're going to be an engineer, right?"
"...yes."
"But tell me, can you actually sit through any of those giant architecture or higher-math books you have on your shelf?"
Emily starts to blush.
"Well yeah. I've read like 75% of them already." She avoids eye contact with you.
"Have you read all of those books, or just the pages with pictures?" You loosen your grip on her wrist.
Emily looks over at you--stunned and surprised.
"Well... well..." She tries to summon up a rebuttal.
"You haven't been honest with yourself, Emily."
"What do you mean?" She backs up against the wall.
"You haven't been honest with the limits of your own intelligence. You like to think that you're a lot smarter than you really are." You step up towards her and press your hand on the wall above her shoulder; hovering over her. "I think you need to be brought down to size."
"What does that mean???" Emily exclaims.
"It means that I'm about to make it to where you won't remember how to read, or count, or even talk. You'll have only a vague idea of what is going on in the world around you, and you're going to be pooping yourself every single day." You explain to her.
Emily stares at you with confusion and contempt.
".............what???"
You put a finger on her lip.
"Shh. Be calm." You say, placing your palm on her head. Before she can wiggle her way out from you, you begin to state your command.
~Your mind will now regress to that of a two-year-old. You will remember the people and places you're familiar with, but will forget everything else.
Your memories will not be erased; merely stowed away to where they cannot be accessed. You can still understand any commands I give you with complete accuracy, including the command to restore your mind to normal.~
You take your hand off her head and reach out your arms to catch her as she quickly loses her balance. She starts uttering a range of nondescript noises, such as "Unn, uhnnn". Before you can even drag her a few feet across the room, her pants are soaking up and dripping onto your legs. The girl verbally expresses discomfort at the feeling of pee flowing down to her socks, so you quickly lay her on the floor and strip her of her now-soaked pants and underwear. You hold the sweats against her crotch for a few seconds to let them catch the last of Emily's wetting episode, then quickly grab the diaper supplies and put them to use.
You wipe up Emily's legs, bottom and crotch; layer her privates with powder and tape her into a plain-white diaper that fits her just right.
From the way things seem, you and this teenage girl--formerly a high-school student, but now probably going to be attending daycare--are going to be spending a lot of time together.