I can't really help any, but I'm definitely watching this thread to learn for my own crayfish. I have not experienced this. Most of what I've read says though that they should get enough iodine from the foods they eat? I don't know though.
It was discolored before it molted but it was underneath the shell because her molt has no visible shell rot and has since just spread everywhere. She is being kept with her babies and I don’t know if I should move her or her babies out
I've heard of rust/brown spots disease in shrimp, and this seems similar, but again, the care I know is based on shrimp. The salt dip/bath is the most used method, but be sure to use unionized salt.
Some people say that either slowly lowering or raising the pH by 1 point over several days may help as the bacteria may prefer it where it is... this is just a may, it hasn't been proven. Some suggest slightly lowering the temperature, as bacteria thrive in higher temperatures. The only issue with this is it will slow your cray's metabolism, and by default, the immune system. However, it often slows down the bacteria more than the immune system.
Here's a link that has it (in shrimp) with some more extreme treatments, but definitely do the salt dips first. Shrimp Diseases and Diagnosis
I dipped her again and used about half a teaspoon for one quart and left her for 10 minutes. she just tried to escape and kind of walked in place and was moving her swimmerets. The first dip was hardly a dip at all i put like 2 grains of salt