Well I realize you said that there is no under heat source, but ditch the rock idea. Under no circumstances should you get a heat rock. That WILL burn her. If it's not a burn it's more then likely scale rot that's gotten very bad. It gets dry and flakey if not taken care of right away and that means she's at, "needs to see a vet right now," status. Even if it isn't scale rot it looks terrible and I've never seen a bubble like that so I can't offer a suggestion to what it is. I think it's safe to say that you need to see a vet. If it is scale rot there are several threads on this forum covering how to help relieve her. Also is that the set up that she is currently in? Because that looks awfully big for a little snake of her size atm. These guys are easily stressed by too much space when they are little like that. And you should have an under tank heater that's hooked up to a thermostat. It will cancel out the worry of a burn if it's on the thermostat. It not only keeps the snake warm but helps with digestion. What are your temps and humidity at? I feel like the scales are a husbandry issue that should be addressed. The bubble is odd to me though. Do you spot clean her tank? Make sure there is no waste laying around?