She stressed that it was just a cameo role, which means she only appears in a couple of scenes.
But she worked alongside Summer Phoenix, which she said was "very cool and interesting".
Till recently all of S Club have been working on their new movie, Seeing Double, and Rachel told us going from one to the other was unexpected.
"We'd just finished filming our movie - so to go onto that was quite weird.
"I was just used to the crew and everything on our set, so to go onto another movie was quite strange."
Suzie Gold is about a Jewish girl who breaks free of her traditional family to get a job at a US TV station.