If she were a baby snake and was loosing weight I would send her back to the breeder. Fact of the matter is, she is a healthy weight for an adult female and has not been loosing a lot of weight. Some ball pythons will fast seasonally for 3-6 months. It is not uncommon nor should it have any adverse effects on your animal. I would not worry about sending her back. Ball pythons are notorious for going on long fasts for no apparent reasons.
She isn't broken and there really isn't a reason to fix her.
You can try giving her a live meal. It could help kick start her metabolism.