Gomez, 27, and Gracie paid tribute to the film's fashion, dressing in matching in feathered capes and long sleeve floral dresses worn in with a thin belt.
However, they opted to have different hairstyles as the Lose You To Love Me singer wore her hair in two loose braids while Gracie decided on an updo.
Gracie is the daughter of Gomez's mother, Mandy who was married to her father, Ricardo Joel Gomez, from 1992-1997. In 2006, she wed husband Brian Teefey, who is Gracie's father.
Ricardo, meanwhile, wed wife Sara Gomez in 2012. The two share daughter Victoria, five.
The pair shared a sweet moment on the red carpet as they embraced for the cameras.
Other guests at the event included the film's stars Idina Menzel and Kristen Bell, who play sisters Elsa and Anna in the Disney animation.
Menzel channelled her character's ice queen wardrobe in a white gown while Bell, who was recently confirmed to return to the Gossip Girl reboot series as the narrator, wore a mauve gown with cut-out detailing.
Other attendees included Evan Rachel Wood, Sterling K. Brown, Josh Gad and Jonathan Groff.
Gomez's young sister often makes cameos on the singer's social media account, with the star notably sharing a sweet video clip back in 2017.
The touching footage showed Gracie telling Gomez "I'm not scared" before the musician responded: "I know because you're fearless right? You're not scared of anything?"
She captioned the post with another heartfelt tribute, writing: "I will forever let my sister know she is strong, bold and beautiful.
"She will be raised to know her voice matters. She is going to understand the importance behind being a leader and inspire others by her truth."