This is why Stephanie is voiced by Kendra.
Stephanie's dad: Stephanie, I have good news.
Stephanie: What is it?
Stephanie's dad: Because you are all grown up at age 12, you are going to get your voice changed to Kendra.
Stephanie: I hope I love my new voice.
Stephanie's dad: Let's go to the hospital.
Sid Phillips: Please Hannah, I don't want my voice changed! All I want to do is stay at home and be friends with Woody and Buzz!
Hannah Phillips: Too bad, Sid! This is what you get for terrorizing my Janie Doll as well as my other toys! When we go home, you are so grounded until you vow not to terrorize any toy of mine! My voice is Kate because I'm mad at you!
Doctor: The doctor is here.
Stephanie's dad: The voice surgery will hurt a little so be patient.
(Censored during surgery)
Stephanie (speaking in Kendra's voice): My voice is now Kendra. I like this voice.
Stephanie's dad: You are good Stephanie. Now let's go home.