Need advice maltese with possible liver shunts.?

Yesterday we took our 7 year old Maltese to the vet and they said it was more than likely that she had liver shunts and/or enlargement of the heart. She has lost 1/2 a pound in 3 weeks and now only weighs 4 1/4. They said if it was liver shunts that all they would do was put her on a LD diet. Which is high calorie, low protein.Their main concern is her weight so they want us to feed her high protein until she gains more and then start her on a LD diet. She also has a flattened trachea so she gets easily choked when eating/drinking that can sometimes cause vomiting. We bought her new dog food with the highest protein we could find. We got puppy food b/c it is suppose to have more calories. The vet also told us about NutroCal. She is the sweetest little dog and it is breaking my heart hearing all of this. We have olny had her since March. If any one could give advice on how to help her get back to her old self I would love it. Also do dogs w/ this suffer?