The Tracy Beaker actress has perfected her routine but is worried she won't pull off the sexy routines she has been given to perform.
Harmer is said to be concerned that she doesn't have the same stage experience as the likes of Kimberley Walsh and Denise Van Outen.
"Dani isn't used to strutting her stuff on stage and is finding that her biggest challenge is trying to be sexy when she dances," a source told The Sun.
"She worried that Kimberley in particular will run circles around her when it comes to the live shows."
Harmer, whose pro partner is Vincent Simone, recently hit out at people commenting on her weight.
The Strictly Come Dancing live shows begin on October 5 on BBC One.
Photo gallery - Strictly celebs in training:
Copyright: Twitter Denise Van Outen