It's difficult to tell if the black spot is really the beginning of scale rot or not. Usually scale rot would be accompanied by a more reddish brown color around the edges of the scales instead of just black, but I would still keep an eye on it just in case. When you were misting was her substrate/bedding getting really wet?

A good alternative to misting every day that you might want to consider is a humid hide. Grab any appropriately sized plastic container, cut a hole in the lid that your bp can fit through, and then take all of the moss you already have and put it inside. Make sure it's damp but never soaking wet. Then your bp can use it during the shed cycle or any other time she feels like it, and she won't be laying on wet substrate all the time.