White, 26, makes her acting debut in Change of Plans, airing on Saturday (8 p.m. ET) on Fox. She plays Sally Danville, a devil-may-care musician whose life changes with a phone call.
"The theme of the movie," she tells PEOPLE, "is unexpected things come into your life, and those unexpected things are the best."
Sort of like going in front of the camera. "Randy's been supervising soundtracks for these Return to Family Movie Nights," White says, "so he called me and wanted to involve me in that so it started there. Never in a million years would I dream it would parlay into me being in the movie!"
"Brooke has three songs she performs on the soundtrack," says Jackson, one song co-written by Idol alum Michael Johns. "And," he adds, "she's really good in this film. You won't believe this is her first time acting, so I think people are going to be pleasantly surprised."
Although nervous when she got the call to audition for the lead role, White says, "Well, I thought I've done one or two auditions before and they turned out all right. It's a lot better when you're not on the Idol stage any more and you don't feel like you are going to be voted off."
In looking ahead at the new season of Idol, White says, "I was on the last season it was the original three judges. It's finally getting to the place where I can watch and not hyperventilate with anxiety."
Jackson promises excitement with Steven Tyler and Jennifer Lopez but says, "Look, it will never be the same as it was. You can't really compare and say, 'Who's going to be the mean one?' Simon Cowell is irreplaceable. I mean, he's an amazing guy, still one of my best friends in the world, and he's doing his thing. But I've got to say, the talent is really strong."
American Idol returns on Jan. 19.