Dustin was turning back to the door, obviously about to open it and call for Mark and June.
"WAIT! No, Dustin, STAY!" Ty yelled, her voice now an unfamiliar but natural sounding feminine pitch. Dustin froze, one had raised to grasp the doorknob. Her command seemed to have stopped him from leaving the room, but it had also given her an idea. She couldn't have Dustin running down to tattle on her every time she tried something new with her powers, so she'd have to make it so he couldn't tell anyone. And since she was feeling so comfortable and happy in her new form, she decided to be nice and make Dustin happy and comfortable with his changes as well.
"Dustin, come here, boy" she patted her thighs and made the wish simultaneously. A whole-body shiver seemed to race over the 16-year-old-who-looked-13 as he turned around. The anger melted off his boyish face as Ty watched, replaced with a dopey grin as Dustin quickly crossed the room. With every step he shrank a few inches, but this time he was unaware of the changes occurring to his body. By the time he'd taken the 10 steps to reach Ty, he only came up to her new boobs, and his shorts had slipped off his shrinking hips to puddle around his feet. Ty noticed that Dustin was actually standing on his tip-toes, and his arches and heels seemed to have elongated and adjusted to accommodate his new stance.
Smaller-Dustin stopped in front of Ty, silently gazing up into her eyes as his butt wiggled a bit under his now oversized t-shirt. Ty reached out and ruffled Dustin's hair, noticing that his ears had stretched into points and were poking through the sandy blond mop. "Good boy, Dusty!" she murmured sweetly, crouching to reach her shrinking brother's changing form. "Do you wanna treat, Dusty? Huh? Wanna do some tricks?!" His whole body quivered at this, and Ty noticed a new furry appendage sticking out the bottom of the shirt and waving back and forth excitedly. "You'll have to SIT, boy!" Dustin promptly sank into a crouch, his hands resting on the floor as his legs reshaped under him until he was sitting naturally on his haunches.
"Good boy!" Ty coo-ed. The t-shirt engulfed Dustin's smaller form, so Ty quickly pulled it up and off her former-brother. She noticed short hairs rapidly growing out all over his naked body, lengthening into sandy tan fur to match his original hair color. His ears had grown as well, even as his human hair shrunk to match his new fur. Darker brown, almost black fur covered them where they stuck straight up on top of his head.
Ty held out her palm "Can you do a ... HIGH FIVE, buddy?!" she laughed as Dustin immediately raised one arm, his fingers having shrunk and reformed into large paws. Tapping her more delicate hand to his furry foot, she reached out her other hand to scratch him under the chin. Dustin seemed to like that, and he stretched out his neck to give her better access. As she stroked, his chin and mouth pushed out into a small muzzle; dark fur raced to cover his face even as his nose darkened and pushed outward as well. Ty rubbed both hands through the fur of his neck and up around to his elongated ears, causing Dustin's mouth to open and a long, flat tongue to roll out with pleasure.
"What a Good Boy you are." Ty said, continuing to pet her new buddy as he leaned his weight against her legs. "A good dog like you would never THINK of saying anything to Mark or June, would he? No. No, you're my most loyal friend, aren't you?" The shepherd dog that Dustin had become slumped bonelessly to the floor and presented his belly, in heaven at all the attention from his favorite human in the world.