The 25-year-old, who's best known for playing Carmen Cortez in the family adventure series, says her latest role in Machete Kills is anything but wholesome.
"It's edgy, it's kickass," the newly engaged star tells PEOPLE of her provocative new role in the film, out Oct. 11. "I think every girl wants to be a badass."
"I'm excited for people to see me in a new light without going over the top," she adds, noting that she's spent years slowly trying to shed her child-star image.
"Making that transition takes so long because you don't want to lose your audience and you don't want to shock them too much," Vega explains. "So you try to take little steps at a time and take on different roles."
But her role as Killjoy in Machete Kills – which is directed by Spy Kids helmer Robert Rodriguez – is more of a giant leap forward.
"It doesn't get more badass than a metal bra and leather chaps!" she says about playing a seductive, no-nonsense vixen who's packing some serious heat.
Killjoy, she notes, is "the right-hand woman" to Sofia Vergara's character, Madame Desdemona, who's "the head honcho at the whorehouse."
Fighting for the Role"I wouldn't say Killjoy is good or bad. She works in the brothel and her job is to make sure that her girls are always safe – whether it's a good guy that comes in and causes trouble, or a bad guy who comes in and causes trouble. And Machete might get in the way of that a little bit, so they may have a little fight," Vega teases.
But Vega admits she had to campaign to get the role. When she asked her friend Rodriguez if he had a role for her in the film, things didn't quite go according to plan.
"He was like, 'Oh my gosh, no – I would never let you do that," says Vega, adding that "I'm like a daughter to him."
She made a compelling case. "I was like, 'Look, I'm always playing these younger roles' – which I love and I'm going to milk it for as long as I can because you can only play young roles for so long," she recalls with a laugh.
Making the Transition"But," she adds, "I also want to make that transition and I want to do it right. I don't think people take me seriously when I walk into a room – and I know I can do it."
Rodriguez asked her to come in and read for the role, which was originally intended for an extra.
"I really had to prove myself. I had to show up on set and own it. And if I gave him even a hint of hesitation whatsoever, he would've pulled the plug and said, 'Get out of here!" she says with a laugh. "Winning him over was pretty cool."