For the past three weeks, Lindsey Haun has been routinely facing a situation few unknown singers ever have to worry about: performing to crowds of 20,000 or more. As one of Toby Keith's co-stars in his upcoming feature film, Broken Bridges, the California native is seizing every unexpected opportunity that's coming her way.

In the film premiering Sept. 7 in Nashville, the 21-year-old Haun is cast as the 16-year-old daughter of a down-on-his-luck country music singer portrayed by Keith. The cast also includes Burt Reynolds, Kelly Preston, Tess Harper and Willie Nelson. After Haun auditioned for film, she not only got accepted for the role but was also offered a deal with Keith's record company, Show Dog Nashville.

For Haun, singing was a prerequisite for the part, and her recording of "Broken" is the first single to be released from the film soundtrack to be released Tuesday (Aug. 29). The soundtrack also features Haun and Keith on the duet, "Broken Bridges." Her involvement in the film led to her guest appearances during Keith's set of his Hookin' Up & Hangin' Out tour featuring Joe Nichols and the new duo, Rushlow Harris.

If Haun's name is virtually unknown to country fans, that's likely to change after Broken Bridges is released and Keith's tour rolls into more than 60 cities. Haun is a newcomer at huge arenas and amphitheaters, but she has plenty of experience in the Los Angeles music scene.

Her father, guitarist Jimmy Haun, is just one of many family members who have encouraged her music career.

"My father played with Air Supply, Yes, B.B. King and even Sheryl Crow when she first started out, so I've sort of been around the industry for a long time," Haun says during a recent visit to CMT's Nashville office. "My grandfather [who performed under the name Rauvaun] was an opera singer, and he had his own show in Vegas and was very successful. My mother was a choreographer, so music has always been around."

Haun's first acting job came at an age when most people are learning to tie their shoes. "I think I was 5," she recalls. "It was a Little Caesars commercial."

By the time she was 6, she was studying with acting coaches, an endeavor that led to appearances on several TV programs, including Alias, Malcolm in the Middle and Third Rock From the Sun. She also starred in the movie Brave New Girl, written by Britney Spears and her mother, Lynne Spears.

In addition to performing music since age 7, she began writing songs when she was 11. That led to her involvement in the L.A.-based band, 7th Fall.

"It was very hard rock, more like Rage Against the Machine with a Pat Benatar vocal," she said. "We had a great time thrashing the L.A. scene. But as an artist, I really feel an urge to expand my boundaries. I was already starting to want to do more melodic things, and Toby's really given me that opportunity. But I still love my band. Those guys are great."

Haun was familiar with Toby Keith's music even before she learned of the Broken Bridges film.

"I had heard his songs before, and I loved them," she says. "My friends absolutely loved him. Even my rock friends loved him. Then when I got the film, I started listening to more of his music, and I was like, 'Oh, I know that song! I like that song.' And I'm just an absolute fan now."

In light of Keith's reputation as one of the more controversial and outspoken figures in the entertainment business, Haun admits she wasn't exactly sure what to expect when she first met him.

"I'm not really afraid of somebody who's very politically vocal," she says. "My mother is very strong, and I really believe in freedom of speech. I think it's one of the things that makes this country great. So anybody who speaks up for what they believe in, I think that's great. Whether I agree with them or not, I think it's such an amazing strength to have -- to be able to sort of throw caution to the wind and just speak your mind."

Broken Bridges isn't Haun's first film with a musical theme.

"They knew they wanted somebody who could sing the ballad, 'Broken,'" she says. "One of the producers -- Sara Risher with New Line Cinema -- knew me through another film I had done. I didn't work with her, but she knew the director. It was the film produced by Britney Spears, and I sang country, pop and opera in that."

After Keith heard a tape she submitted, he also signed her to his Show Dog label. "Toby took an interest in me, thank God," Haun says. "I love the fact that I'm working for him. He's such a great boss."

Keith co-produced the film soundtrack with Nashville veteran Randy Scruggs. Together, they're also working with Haun to gather material for her debut album.

"Most of my experience is live and at the rock clubs," she says. "Now that I'm stretching out, it's really exciting. I'm getting used to what my process is in the studio, and they help me out so much. The three of us have a great working relationship."

During Keith's concerts, Haun performs her two songs from Broken Bridges after the audience watches a clip from the film.

"Every time I hear about a new development with this project, I want to cry," she says. "It's just the perfect situation. For something like this to come to me is so humbling."