Looks like there was a lot more to Charlie's change in dietary habits than we realized. Apparently Charlie is a lot older than we thought. I showed the earliest photos we have of her to an online veterinary assistant, who is of the opinion she was 3 or 4 at that time. Since her back half was very underdeveloped we had assumed that she was less than a year when we found her. That would put her at 9 or 10, but after checking the meta data from the photo, I discovered it's not 6 years since it was taken, but 8. So Charlie is actually 12 or 13 now.
Veterinary assistant seems to think that due to her past injuries and other physical problems, she's now suffering from acute old age and her organs are starting to shut down. She hardly eats at all anymore, has lost considerable weight and grows weaker day by day. Her prognosis is not good.