Some snakes starting eating one prey item, the don't like to change. You may have to find a mail order place to get frozen chickens. You could also try a rabbit. As for getting her to eat rats, try getting some used rat bedding from your local pet shop and put it in her enclosure. Let her smell it for a week or so and then try. That's the best advise I can give--don't know anything about burms. Good luck.