Losing 300 grams in that time is a bit puzzling. I've had cornsnakes go off food for 3 months at a time and not lose more than 50 grams...even being very active looking for a mate. While balls of either sex tend to stop eating during the winter months, males are more prone. Just because a breeder said it'sfemale doesn't mean that a mistake wasn't made. Mistaking a male for a female is done quite often because the probe wouldn't go all the way in. I usually probe multiple times if sexing (or pop several times if popping) when I say it's a female to be sure. You won't probe a female as a male unless you go too far, but you can easily probe a male as female. Have you tried feeding live? Many balls will only take live, or will go from taking f/t to only live. You might also try hamsters, or African soft furred rats as well.