How do you check the temperature of the heat pad ?
I am sorry to say, but checking twice the day is not sufficient. I don't know of any heat pad that runs in a safe zone for a snake. All of them tend to get to hot if they aren't regulated. There is one brand that claims they won't, but I have had them, and yes they do!
That looks like a deep burn. Remember, what feels warm to us, is usually much to hot for a snake. Our bodies run at 98 degrees. The heat of the pad should not be higher then 90 degrees. So even if our hands are a bit colder then 98 degrees, if the pad feels warm, its probably to hot.
If your mom was a vet tech she can clearly see this is bad. There is only so much you can do externally. The layer of scales is gone in places, it is raw skin you see. Infected , too. Things like that quickly go toxic.
I understand money issues. I do. But there is nothing else I can say other than that you NEED a thermostat. There simply aren't any what, ifs and maybe's about it. You can see why. This is a living being and some things are simply not negotiable. You can get a thermostat on Amazon for $30.
I suppose you can keep treating at home if you have no other option. Us fussing at you won't change the facts. But I implore you to try to figure out a way. Make payments at Vet or to family members or friends. Even if a new snake is cheaper then the Vet, this is YOUR animal and it is suffering. You took it on, its your responsibility.
I'd like to sugar coat it to make you feel better, but in this case, there simply isn't any sugar coating.
Keep it clean and keep treating it. Do not use all those different methods at once, the area is raw and some treatments damage healthy but fragile and exposed tissue..