Slated for a young girl’s 15th birthday, a Mexican Quinceanera celebrates virginity and coming-of-age with the extravagance of the ritziest bat mitzvah. In Richard Glatzer and Wash Westmoreland’s appropriately titled film (that would be “Quinceanera“), emphasis on all the trimmings–a hummer limo, a brand new dress–causes a rift between Magdalena (Emily Rios), an Americanized 14-year-old, and her old-fashioned father, a storefront preacher who moonlights as a security guard so that he can pay the bills.

“It’s the Quinceanera wars,” Westmoreland said at a recent press event I attended, where he joined Glatzer, Rios, and co-star Jesse Garcia to talk about the film, which won both Special Jury Prize and Audience Award at this year’s Sundance Film Festival and opens in limited release on August 4th. “Magdalena’s father wants it to be more spiritual and traditional but Magdalena’s a modern American girl.”

According to one modern American girl, materialism–in the movie and in real life–is synonymous with growing up. “What are you going to do, just stay 10 years behind?” Rios asked. “Centuries ago it wasn’t about having a hummer limo. Things we see on TV, kids want that type of lifestyle themselves. They don’t think of religion.”

But there’s a bigger problem these characters must soon face: Magdelena’s unexpected pregnancy, the result of, in Westmoreland’s words, “lots of teenage wriggling and a little too much enthusiasm, but no sex.”

“We were thinking, ‘We don’t want to retread a story of a young girl getting pregnant,'” Westmoreland said. “I’ve been in a sex education class in the north of England in the middle of 1981, and the nurse had told us about this strange way of getting pregnant.”

“It gave her a kind of pride–she didn’t realize she was even at risk for being pregnant, and therefore she had this tough spirit,” Glatzer said. “I had two different people come up to me after screenings at Sundance and tell me they were products of virgin birth.”

But Magdelena’s father doubts her abstinence, so she moves in with her great-uncle Thomas (Chalo Gonzalez), and gay cousin Carlos (Garcia). Initially at odds with one another, Carlos and Magdalena eventually bond as community outsiders.

Off screen, Rios and Garcia clicked instantly and were surprised to discover that they were both former Jehovah’s Witnesses: Garcia questioned the practice when he enrolled in a theology class in college (“I ended up learning a lot of different things about different religions that I liked,”), and Rios was presented with her first birthday cake when she turned sixteen on set. “I think I wouldn’t have dealt with the things I dealt with if I continued being an active member in the congregation,” Rios said. “I went through some tough times when we weren’t practicing anymore. I was born into the religion–going to church four times a week, dedicating your entire life… I felt a little liberated. It’s not that I didn’t know any better, I just didn’t know any different.”

Regardless of religion, Rios identified so strongly with Magdelana that she didn’t feel like she was acting. “Whether it’s Jehovah’s Witness or not, I know how strict families can be,” the actress said. “My parents always taught me everything goes by the bible, so it was a rebellion. ‘You want to talk to me about the bible, you guys aren’t practicing anymore, so what are you trying to tell me about it?’ It was just a big old clash. In the end, you’re going to accept one another because family is basically all you have.”