They get skinny after laying eggs, but from the description I highly doubt that is the case. It sounds like an underfed snake, the pushing could very well be a result of looking for food. I'd get her to a vet for a full check up including for a potential RI since burmese are notorious for that. Get a fecal done if you can when you can as well, they aren't too expensive. Make sure you have her very well QT'd. Burmese are not suppose to be morbid obese, but if scales can pinch together its bad news. Make sure you keep her warm and humidity up. And don't start with giant foods, work your way up for sure.