The movie follows the story of Mary Baxter, a young dancer who had four children -- daughters Carolina, Austin, Dallas and Baltimore -- from four different fathers. When Mary tragically dies, her estranged kids reunite at their family home in New England. The lead roles are portrayed by Jacki Weaver, Stana Katic, Jess Weixler, Michelle Trachtenberg and Troian Bellisario, respectively.
In a sneak peek clip from the drama, Gerber -- who plays the young version of Carolina (Katic's character) -- can be seen sitting at a table with her onscreen siblings during a flashback scene. When her mother gets up from the table to go drink with a guy, the brunette beauty goes into full responsible mode and encourages her younger sisters to leave with her.
"This is a jazz club, Mother, with cigarettes and booze," Gerber exclaims in another clip, responding to her mom's request to sing "Happy Birthday" to Dallas. "We're little girls. Don't embarrass us."
"Who wrote the rule book that girls celebrate their birthdays at Chuck E. Cheese?" Amy Smart, who plays young Mary, responds, with a full glass of wine in hand. "The Baxter girls write their own rules."
See more sneak peeks in the video below.
ET caught up with Gerber at the film's premiere at the Paramount Theatre in Hollywood, California, on Wednesday, where she opened up about what it was like to act for the first time.
"This was an incredible experience," the model explained. "I could never imagine something better as my first role."
Sister Cities premieres Saturday, Sept. 17 at 8 p.m. ET on Lifetime.