Transcript for Christie Brinkley's daughter on taking mom's 'Dancing With the Stars' spot
Reporter: The 28th season of "Dancing with the stars" opened with its usual fanfare and fabulous sequins. A star-studded stage filled with show-stopping costumes and moves with all eyes on that mirrorball prize. But as celebs like Sean spicer -- hold tight Lamar Odom. And James van Der Beek showed off their ballroom skills there was one high-profile star missing. Supermodel Christie Brinkley was sitting in the audience instead of dancing. After breaking her arm during rehearsals. Uptown world forcing her to bow out days before the premiere. Oh, oh, oh, oh, oh but she watched on with pride as her 21-year-old daughter and fellow "Sports illustrated" model sailor brinkley-cook seamlessly filled in at the last minute. Strutting her way through "Uptown girl." Uptown girl one of her mom's most iconic moments. But getting to this point wasn't exactly the plan. Tonight's episode revealing the rush and chaos behind the 11th hour swap. My mom's had three weeks to prepare this dance and now I have three days. I mean, you got on a flight out here to support your mom. I'm literally about to take off, two minutes to takeoff and my mom calls me and says sailor, you need to save the day. And I was like what do you mean save the day? And she's like they want you to fill in for me. And I was like, mom, I'm taking like the wheels are up in 30 seconds. And I landed to texts and e-mails and everything like all right, going into your fittings, going into rehearsals, all this. And I was like, what? You didn't really have a choice. I freaked out and I was like I don't know if I can do this, I'm so scared. Then I met with everyone from "Dancing with the stars." I felt this high of like just attacking something I'm so afraid of. It seemed so incredible to do. Oh, oh, oh Reporter: Christie was gearing up for her big debut with my former partner pro Val chmerkovskiy when watch here, one slip in rehearsal brought her crashing down. I think I broke my arm. I swear to god. No way. You know, that's the nature of the show. You never know what's going to you just kind of roll with the punches. Reporter: It wasn't just broken but shattered. The 65-year-old headed to surgery on her wrist and arm. I knew she was 65. And I had a really good feeling that she was going to do good for the older people. Uptown girl Reporter: But the show must go on. And sailor fox-trotted right in. Her mom's costumes didn't even have to be altered. And she sashayed out of Christie's shadow and into her own spotlight. Wow! Reporter: It was a triumphant moment for the young cover girl who once struggled to find her own identity. Juju Chang spoke with sailor about her body image issues last year on the set of her "Sports illustrated" shoot. I've struggled with my body since before I could remember. I've always had issues with it. I've never truly accepted it except for recently. And I'm still growing. I'm still understanding. Reporter: And what do you think, just to help other young women? How did you get over that? I mean, it was a long battle. I went from being too fat to too skinny to too muscular to -- I've been everything in the book. And especially growing up in the public eye with my mother, I mean, I was always criticized. I was constantly criticized. So I had to realize that there is no one except for myself that I have to live for and love. Reporter: Sailor, seen here with her sister Alexa Rae Joel and mother, comfortably posing for "Sports illustrated's" 2017 swimsuit edition. Now sailor's hoping into spire oods as she takes to the dance floor and most importantly makes her mom proud. I'm doing this for my mom, especially the first dance, and I'm trying to learn it to the extent that it will make her happy and make her proud to see. She loved doing this. She loves dancing. She loves performing. And this was a dream. And getting hurt was her worst nightmare. Reporter: Christie's injuries aren't the first to shake up the stage. In 2007 Marie Osmond passed out for 30 seconds after performing the samba. And singer normani rolled her right ankle during rehearsals in 2017. I even know from experience. I hurt my pelvis and back before my season finale performance. But managed to push through with the help of the show's physical therapist. And when she wakes up and makes up her mind with an entire season to go before the finale there is still so much that can happen. But sailor is taking everything in stride. I mean, first time I got out there for a rehearsal I screwed so it's like, you know, I am afraid of that obviously but I'm going to do my best. And if I screw up c'est la vie. She scored 18 out of 30 but proved to the judges she was the perfect substitute for her mom sxwlp she cries every five minutes the fact I'moing this and the fact I'm taking over. She calls it's silver lining, we found the silver lining in a terrible situation. And you're it. And I'm in I guess. Reporter: Making up her mind that uptown is the only direction to go. I'm so proud of her. Reporter: For "Nightline" I'm ginger zee in west Hollywood.
This transcript has been automatically generated and may not be 100% accurate.