In town lending her support to The Runaways, the biopic about Jett's '70s band The Runaways, the singer took the stage in a one-piece sequined leotard and sneakers.
But it wasn't her fashion choice that got the crowd going – it was special guests Kristen Stewart and Dakota Fanning, who star in the movie premiering at the Sundance Film Festival.
After thanking the film's director, Floria Sigismondi, and other folks who worked on the film, Jett gave a shout-out to Stewart and Fanning who'd come up onstage, and thanked them in front of the audience.
Stewart, in ripped jeans and a dark hoodie, and Fanning, in sleek dark outfit and heels, waved and smiled as the crowd broke into thunderous applause. The two soon retreated backstage where they finished watching Jett's incredible show out of the spotlight.
The Runaways premieres Sunday at the Sundance Film Festival.