Shell rot is frightening to hear. And shell rot is actually shell fungus that is out of control and has become infected. An active actual bacterial infection. Not just simple fungus any more. The shell rots, smells badly and starts to break down.
Shell rot is very serious and much harder to treat.
You have shell fungus.
It happens with Redfoot because of their need for humidity and them loving to lay and sleep in wet areas.
My group get it every summer like clockwork. If caught fast, it goes away quickly. It's no big deal.
Apply a smear of athletes foot cream on that area every 2 days for about 10 days. The fungus will die. But the damaged shell carapace will take many months to LOOK healed.
You can use the "dollar store" brand of foot cream or the stuff that costs $12. It all works.
You will likely see it again in the future.
So. The short answer is no.
You do not have shell rot.
You have shell fungus. And it's not yet very bad.