Her ukulele is the same size, but Grace VanderWaal has grown up plenty since she first appeared on TV as a 12-year-old “America’s Got Talent” champion in 2016.

Now, after releasing music, touring the nation and modeling, the singer/songwriter has a new role as the titular star of the Disney movie “Stargirl” (streaming Friday on Disney+).

You'll probably recognize her, even though she's grown nearly a foot in four years.

“I don't really know exactly how tall. I think I'm 5-foot-8 or something like that,” says VanderWaal, 16.

We caught up with VanderWaal right after she performed on “Jimmy Kimmel Live!” to talk about her new movie, forthcoming music and why memorizing a monologue was easier than playing her uke on the set.

Q: You just played your moody new single, “Today and Tomorrow,” accompanying yourself on ukulele. Sticking to your roots with your signature instrument?

Grace VanderWaal:I actually didn’t (write the song with the ukulele in mind). I was just singing in the studio and the producer pulled out a ukulele and started kind of like jamming to it and then we were just like, “That sounds really good.” The whole song just kind of happened. I wrote it while I was filming “Stargirl,” and I showed director Julia Hart and I guess she liked it. So it’s in the (end credits).

Q: In “Stargirl,” you play a teenager who was home-schooled but becomes a good-luck charm for a high school and serenades classmates with her ukulele. How is playing as Stargirl different from performing as yourself?

VanderWaal: It's so different! Just because I'm not telling my own story. You know what I mean? (At my shows), I know exactly what I want people to feel. But when you're telling someone else's story, it's more difficult to try to figure out what they would have wanted people to feel.

Q: At least you had plenty of experience playing music before you did it as Stargirl. But what was it like to memorize and perform a monologue? There’s a big speech for your character in the movie.

VanderWaal: That was the easiest part. I feel like I'm such a serious person. And I was just saying probably the truest emotions of my personal feelings in the movie (when my character makes a speech about appreciating the beauty of a flower growing). It read easily for me, and I feel like you can see that in the movie.

Q: Last year, you made it sound as though “Stargirl” was a one-off for you. Have you changed your mind about pursuing acting?

VanderWaal: Yes! I learned so much while making this movie, and I'm ready to apply it and see if I can be good. You can't really do anything to the best of your ability on the first try or even the second try, but I do want to see. I like to be good at things. If I'm doing something, I want to abandon it knowing I did the best I could. There’s this one role that I really, really want, but I don’t want to talk about it because there’s literally like a 30% chance that I’ll actually get it.

Q: You’ve acted in your own music videos before this movie, but you have your first onscreen kiss in “Stargirl.”

VanderWaal: That was a big deal. There were closed sets for every scene like that.

I mean, I was 14, very, very young. It's not like I'm a grown-up and I've had like tons of boyfriends, you know? So of course I was nervous, but we all made sure we were just being our characters and (co-star Graham Verchere, who plays Leo) was professional. I think the nerves actually worked well for the movie because Stargirl is supposed to be like that, she’s not some player.

Q: Stargirl has plenty of glittery and playful fashion, while your style has gotten pretty sophisticated through your modeling and recent trip to Paris Fashion Week. Were there any Stargirl items that Grace VanderWaal would really wear?

VanderWaal: There is one outfit that Grace VanderWaal would actually wear in real life, and it was during a dating montage where she was practicing her speech in front of Leo: the pom-pom vest. It didn’t get that much screen time, but I felt so comfortable and confident in that outfit and I would absolutely wear that.

Q: Are you planning any live shows this year after “Kimmel”?

VanderWaal: (Coronavirus) is actually really impacting my schedule. We're afraid that two upcoming festivals I was like looking forward to for months (including BottleRock Napa Valley in May) are probably going to get canceled. It's really messing up a lot of things for a lot of people. But I understand. I mean it's pretty crazy.

Q: You’ve put out a steady stream of singles since your 2017 debut album “Just the Beginning.” Is songwriting still a priority for you?

VanderWaal: Yeah. I’m preparing for Volume 2 of my EP, and I like the music that I’m making, so let’s see how it all turns out. It’s really good, but I wouldn’t say I’m entering a new direction. I’m not rapping or doing new genres.

Q: So we will hear more ukulele?

VanderWaal: Possibly.