From what I can see, it looks like a thermal burn. She may have burrowed under the substrate and down to the heat pad. I would say to remove the substrate, put down some newspaper and put neosporin on her belly once or twice a day until her next shed. Keep her cage very clean during this time.
I stopped using 'Bed-a-Beast', et al, because it was getting into the snake's mouth, pits, nostrils.... not a good thing. If you really want to use a substrate that is natural and holds humidity well, go with cypress or eucalyptus mulch.
Good luck with her.