shell problems

[ed17]

hi,
i have noticed that one of my three toed box turtles is beginning to have a rough, somewhat flaky shell. The shell is firm and has no discolouration. Some sections of her pattern are beginning to rise slightly, so the edges are able to be picked at. Her eyes are clear and her skin is healthy. I was wondering if anyone knows why this is happening, any suggestions would be greatly appreciated.

Thanks,
ed