You decide that, despite not wanting to inflict pain on her, you still want to do something. You think over what you want to actually do. You aren't willing to hurt her, or put her in extreme discomfort, or anything of the sort. You also want something unique, you don't know why, but you want it to really stand in her mind.
You think of your science class yesterday, your teacher let you play with a weird metal called Gallium, which you could melt in your hand. This strikes you as an interesting idea. You think about it further and you realize that every single time you've held one of them, their touch has felt cold compared to yours. Their body temperature must have somehow scaled somewhat with their size. Contemplating this, you whisper to the voice, asking for Gallium. A good sized chunk, easily bigger than one of the girls, falls into my hand. I place it on the ground before it starts to melt. You get up and find some gloves and a paintbrush, then you sneak back into the room. Sadie's too engrossed by watching Rachael to notice you approach her, but she notices soon enough as you grab her.
Thinking, you decide that you can blame the voice, after all, no one else can hear it. Once her screams calm down, you explain that the voice didn't like how much she seemed to enjoy watching them get hurt, so it decided to punish her. On the voices part, it only giggles, it's vaguely disturbing that something you chose to do is making it happy, but you decide to ignore it for now. Sadie struggles and pleads with you, but you aren't planning on letting her out of this.
You begin to strip off her clothes, her shirt, her shoes, her socks, her pants, her bra, her panties, until she is completely naked. Then you put on the gloves, holding her tightly in one hand as you put the glove on the other, before placing the Gallium in the now empty bowl from earlier and breathing on it. After a bit, your breath causes the Gallium to begin to melt. You take the paintbrush and pick up some of it, before swiping it along Sadie's skin. You proceed to do this until every swath of her skin is covered, save her face, then you pull off a glove and grab your iPad with the other hand, locking the door, place her down, and wait. He first action is to pound on the door, on course with what you'd expect, but with it locked, she backs away. Looking around, she stands in the open and covers herself, seemingly not sure what to do, and looks around with a frantic expression. She looks like she finally decides where she wants to go, but she doesn't move anywhere. A look of horror comes over her face as she realizes she's unable to move. You watch her struggles for a bit, then you go and grab a plastic cover, the type that goes over ID tags, and you cut a circle. Then you cover that with Gallium and wait for it to freeze. Taking your platform, you pry Sadie off the floor and place her on your makeshift pedestal, and use Gallium to glue them together. Lastly, you take the thinnest paintbrush in your collection and begin to carefully trace everything but her eyes. As you get to her mouth, she wisely shuts it. You wait, and the gallium freezes, finishing your statue.
Not wanting it to melt, you place it in the fridge for a bit, along with the gloves, then you wrap it in a hand towel and carry it with you to go visit Alex.