Sounds like there might be a couple of issues that might help out. If you have a UTH without a thermostat that could be very dangerous for your snake. The temperature under the substrate could be hot enough to burn or kill your snake. It also sounds like the food you have might be too small. I think an 8-12 month old BP should be taking at least pups or wean rats. If she won't eat f/t you might have to try live to get her eating and then switch her over later. Best of luck!