Is her bum raw like diaper rash? If it's not infected, try using a small amount of Vaseline. Vaseline will create a barrier to keep the feces away from her skin and from sticking. I've found it works the best of anything I've tried. Try a tiny spot just to make sure she doesn't find it interesting and chews at it. The majority I've used it on have been fine, one girl decided it had to come off.
How old is she?
* * * Nancy * * *
Retired from breeding
Rescue contact for both the Hedgehog Welfare Society and the IHA
Rescued over 70 (and counting) hedgehogs needing a new home