I think it might be shell rot. The large white patch is from a scute that came off brushing her shell two days ago. The shell feels soft in one spot. There is no foul smell. Anyone know what's wrong?
It's a bone layer. It will likely also come off (and expose some flesh) but hopefully scar tissue will develop over it. If not or if there are other trouble areas, then a vet visit would be a good idea.