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Selena Gomez, the Wizards of Waverly Place actress and teen-pop singer, is doing some major growing up.

First up, the 18 year old, also known as Justin Bieber’s main squeeze, is co-hosting Sunday night’s MuchMusic’s Video Awards in her very first appearance on the show during a year where badasses have been confirmed among the performers (Snoop Dogg) and presenters (Colin Farrell).

She will also perform alongside a lineup that includes dance-pop provocateur Lady Gaga, who wowed with her “flaming boobies” display during an MMVA performance a couple of years ago, and raging blues-rockers The Black Keys.

“It’s exciting and scary at the same time because (Wizards) was my safety net. That’s all I really know so it’ll be interesting to detach from that and be on my own,” said Gomez on the phone from Los Angeles recently.

“I don’t think (the transition from teen to adult in show business is) easy … Just because I have my summer kind of booked, I never want to assume that I’ll be OK. So I always want to be prepared. I’m a little nervous but, at the same time, I think I am in a good place. Hopefully, I’ll be able to make the transition the right way.”

And she claims to have not learned anything from the uneasy teen-to-adult transitions of fellow Disney teen stars Demi Lovato — who went to rehab for “emotional and physical issues” related to her recent bi-polar diagnosis — and Miley Cyrus, who was criticized for acting and dressing provocatively and smoking a bong in pictures posted online.

“No, I think everybody has their own choices and everybody wants to grow up their own way,” said Gomez, who says her fans, friends, family and professional team keep her grounded.

The closest she’s come to a scandal was a June 9 hospital stay after complaining of headache and nausea after appearing on The Tonight Show with Jay Leno. She was released shortly after and said she was feeling better.

Gomez will say she’s “very nervous” that the MMVA gig is her first time hosting anything and that she’s going to be “a fan just as much as the people watching.”

Just don’t ask her if Bieber, who appeared on last year’s MMVAs and is up for two awards this year, is coming as her date.

“I’m sorry, no personal questions,” said a publicist listening in on the interview.

Back to her hectic work schedule: The high profile MMVA gig for Gomez coincides with her transitioning out of her Disney series Wizards of Waverly Place, now in its fourth and final season; Selena Gomez and The Scene’s third album, When the Sun Goes Down, due June 28; her second major feature film, Monte Carlo, opening July 1; and her first-ever North American headlining tour, which arrives in Toronto Aug. 23 at the Molson Canadian Amphitheatre.

“(The album) is pretty much the same kind of vibe — it’s dance, it’s techno, it’s really fun,” Gomez said. “It’s a little bit older but I’m still in my comfort zone. It’s kind of fun to grow through my music.”

As for her tour, she’s already talked about having a Britney Spears tribute as part of the show. “It’s going to be the first time that I’m able to do a tour so it will be fun and it will be different and I want it to feel like a whole party atmosphere. Hopefully, my fans enjoy it,” Gomez said.

Meanwhile, the romantic comedy Monte Carlo sees Gomez, Leighton Meester (Gossip Girl), and Katie Cassidy (daughter of David) star as three American girls on vacation in Europe who pose as wealthy socialites in Monaco. Gomez was cast after appearing in her first film, 2010′s Ramona and Beezus.

“I had worked with Fox before and so the people who produced (Monte Carlo) kind of had me in the back of their minds, which was very sweet. I met with the director and I was blessed enough to do this film with them,” she said.

In Monte Carlo, she must have a British accent for her socialite character, and we wondered if she was feeling more confident as an actress as she moves from TV to film.

“Yes and no. I like that I’m doing things that I’m not used to and kind of being challenged. But, at the same time, I love acting so I love being able to try new things,” she said.

And the actress she watches and wants to be like? Wouldn’t you know it, she’s a Canadian.

“I love Rachel McAdams,” Gomez said. “I think she’s so talented.”

In the meantime, one major chapter of Gomez’s professional life has come to a close. And at the time of this interview, she had just finished shooting Wizards’ last episode.

“It was really hard. Everybody was crying and they wrapped (the actors who play) my brothers at the same time on my show so it was nice to kind of end it with the people I started with — it was sweet,” said Gomez, who shot the pilot when she 13. “They’re my second family. They definitely went through a lot with me.”

And she thinks fans will be happy with the way the series ends. “I definitely do. I loved it. It made me feel very warm so I hope that they agree.”