Hello I am Dr. Joey. Thanks for trusting me to help you and your pet today. I am a licensed veterinarian with over 16 years of experience. I look forward to working with you.
I am so sorry to hear your dog is experiencing this. The muscle mass loss is probably direction related to her low to no appetite and weight loss. With a sudden lack of appetite over the past few days to weeks, this may indicate a larger medical problem. I always recommend we try to determine if there is something we can treat first before we assume this may be due to age-related loss of taste. So, if not already done, she needs to see her veterinarian as soon as you can arrange this for a physical exam and some testing. At a minimum she needs lab work (chemistry panel with electrolytes, thyroid screen, urinalysis and complete blood count +/- stool check). She may also need some imaging based on this testing (radiographs or ultrasound). With this information we can usually tell if there is a larger problem going on.
AS far as diagnosing this online, I am afraid I cannot do this. The loss of appetite is such a vague sign that could indicate anything from an organ problem (liver, kidney, pancreas) to endocrine issue to cancer to foreign object in the digestive system to parasites to infection (fungal, viral, bacterial) and the list continues. Our hope is we can find something easily treatable such as a terrible urinary tract infection.
In the meantime, you are doing a great job tempting her to eat at home and please continue. Some dogs will go for blander foods like pureed people baby food (chicken variety) or canned meat products, but also offer her favorites. You may also try to address nausea with use of something like famotidine. If she was my patient I might recommend you try half of the 10-mg tab every 12 hours. It doesn't have any bad side effect and does a great job reducing sour stomach.
I am at a point I need to know what questions you have. I hope that the information I provided has been helpful.
Please let me know if for any reason you need further clarification, have more questions, or were expecting a different type of answer.
If you received all the information you needed, then kindly submit a rating.