The 'Never Let You Down' singer makes her major motion picture debut in the erotic movie, taking on the role of Christian Grey's sister Mia.
However, she failed to turn up to yesterday's UK premiere of the film, despite tweeting the day before: "@FiftyShades London premiere tomorrow! It's a blink and you'll miss it role,but I'm so happy to be part of it!"
Rita has already seen the film, tweeting a week ago she'd enjoyed a private screening alongside her pals.
The character of Mia has a small role in Fifty Shades of Grey but a bigger presence in the following two books: Fifty Shades Darker and Fifty Shades Freed.
While Rita skipped the premiere, the movie's stars Dakota Johnson and Jamie Dornan braved the freezing cold temperatures alongside director Sam Taylor-Johnson and the book's author E.L. James.
Fifty Shades tells the story of dominant businessman Christian Grey's relationship with naive student Ana Steele, a relationship that begins with a bondage contract.
It's been rated 18 in the UK because of its sexual content.
The movie opens to the public today - just in time for Valentine's Day! - and has already broken records with ticket pre-sales, with Odeon cinema chain saying one has been bought every seven seconds.