After thinking it over for a minute, you finally decide what to do. You grip the wand and mentally tell it to make her butt grow to a nice plump size. You sit next to her on the edge of the bed, and watch the magic happen.
Jessica was still pleasuring herself, using one hand to intensely plunge the vibrator into her clit while the other massaged her now massive breasts. After a few seconds she said "Oohhh, my ass is tingling!" You both look down to her flat ass, and watch as it starts to fill out some. Her butt continues to grow a little, fattening up to a nice apple bottom. She pokes a cheek, her finger sinking in a little bit. She stands up and walks over to the mirror, completely forgetting about the vibrator still in her clit.
She stands in front of the mirror and watches her asscheeks fill out the last little bit before stopping. She grabs a cheekfull with each hand and gropes her butt. She smiles a little before turning around and twerks. You sit there, surprised, for you had no idea your sister secretly wanted to twerk. After a minute she stops and stares at her new figure in the mirror while fondling herself.
While you watch her grope, you stay on the bed. Eventually you decide to keep things moving. What happens?