If you're absolutely sure there's nothing medically wrong with her, you can try taking her out more often. Instead of every hour or two, take her out every five to ten minutes, regardless of whether she needs to go. Don't wait for a signal.
Does she only do this when you are not around?
Have you tried cleaning her crate with something like Nature's Miracle? If not, the odour may still be present which could be encouraging her to pee there.