Do you mean the UTH is plugged into a thermostat? A thermometer only reads the temperature, it doesn't regulate the heat.
At her size, if she refuses, I wouldn't handle her or offer a meal until 4-6 days later or so, and see if she takes it. Overhandling could make them refuse food too.
Anything you've changed, including bedding, could cause them to refuse... I had a young BP about that size refuse food a couple times after switching her from paper towel to aspen. Then once I switched back to paper towel, she started eating again