The ex-Emmerdale actress, who is paired with Robin Windsor, suggested that she had impressed producers by mastering sexy moves for a recent stage appearance.
"I did a play that involved a pole dancing scene this year and I think one of the Strictly producers saw it, so I got the call," she told the Radio Times.
"I was a bit nervous because all the dancers are so dinky and, well, I'm not."
Riley also admitted to being apprehensive about whether Windsor would be able to handle her larger frame.
"I have a right to dance whatever my size," she said. "[But] I am so worried Robin isn't going to be able to get me off the floor."
Riley previously warned notoriously nasty Strictly judge Craig Revel Horwood to "be afraid" of her, as she "can throw a good punch".
Strictly Come Dancing's first live performance show airs Friday, October 5 at 9pm on BBC One.
Photo gallery - Strictly Come Dancing couples: