what do you think is wrong with my ball python's belly

[Vypyrz]

It looks like a scar from a thermal burn. But birth defect isn't out of the question. I've seen a few rescues that have scarring quite similar to that because of being burnt.

I agree with that statement. Without knowing the full history of the snake, it's going to be hard to know for sure why it's belly is like that. But, I'm sure she appreciates you for getting her out of the tank with the Boas...