Check her over carefully and make sure she doesn't have mastitis(infection of the mammary glands) This could be making her feel sick, and needs to treated promptly.One other idea is to listen to her stomach as well and see if it sounds gurgly, which could indicate tummy problems(ie gas, which you could treat yourself with infant simethicone)
Usually new moms have a good appetite, and appreciate extra treats when they're nursing. Any chance that the batch of pellets you have could be off?
Lori