I'm going to agree and say it's a burn - just like when a person gets a burn and our skin blisters - your snake has blisters under her scales. And, just like in a person, when it blisters, it's indicative of a pretty nasty burn.

I've treated this before in a rescue: twice a day you will need to clean the area gently with soap and water, and then apply bacitracin to the afflicted area afterwards. Gently rub the bacitracin in to the scales. You can also use neoproxin, though I wouldn't recommend using anything that has a numbing agent. Eventually she will slough the blisters during a shed, but you need to treat up until this happens.

First things first - remove the cause of the burn! Either get a thermostat or remove the UTH - move it to the side of the tank if necessary. She will not learn from getting burnt once, and will continue to hurt herself in an attempt to get warm!

Hope this helps.