I’ve just had a look at RC gastrointestinal low fat
and the fat is 7%. I wonder if the vet wants your dog to stay on this food because it is quite low for long term use. Very few commercial foods have such a low fat and that’s because dogs need fat in their diet. The low fat products tend to be light weight loss ones intended for short term use although sometimes dogs do stay on them long term. The protein in the RC is only 22% so topping up with chicken is a good thing.
If you feel that you would like to try your dog with a non prescription food we can help you source one using the Dog Food Directory. Your vet would need to tell you what percentage of fat and protein (dry weight) would be suitable. Digestibility is key as dogs find it easier to utilize animal protein. You therefore want to be looking at products with the protein (meat) source named and right at the top of the list. All the ingredients in the list need to be crystal clear. This thread
might be useful for you.
I hope that the behaviourist can help your little dog and that she soon feels more comfortable with you. My friend adopted a little dog similar to Ruby and it has taken a long time for him to lose his nervousness but he has come good in the end. She had to be very patient with the little lad.
Edit: Prescription diets
is an article written by David and which might be of interest to you. Prescription diets can be useful, mostly to help dogs get over a period of illness.
Royal Canin website mentions that the food you currently have is for acute and chronic pancreatitis. If your dog had a one off episode of pancreatitis it would be classed as the former and hopefully she will be ok as long as she has a suitable food. If this is the case, perhaps the vet would agree to a change of food as long as it has the correct fat/protein content. This food is said to be low in fibre and some dogs with colitis benefit by having good quality fibre in their diet as it promotes gut health. As mentioned, discuss with your vet and if you need help, please post back.