Funny you should post this...well, not funny, but I noticed one of my girls limping yesterday too. I picked her up and looked her foot over really well but didn't see anything out of the norm.
Be sure that the pad of her foot isn't overly squishy with a hard spot in it. That would signify a possible bumblefoot. Look it up, cause I don't have any experience with it but I'm watching my girl closely for this.