Have you joined the liver shunt and mvd group yet?
Liver_Shunt_And_MVD_Support : Liver Shunt & MVD/HMD Support
You will get excellent guidance there, and there's a ton of information in the FILES that you can print up and take to your vet.
On pups and younger dogs, the success rate is very high, but the older the dog gets, the higher the risks because the liver has been damaged for a long time. There are more complications with older dogs, but I do know of several dogs who had surgery above the age of 2 and survived.
My yorkie does have liver problems and is medically managed with a special diet, supplements to support his liver to the fullest, and lactulose. My yorkie is now 4 yrs old, and he is doing great!!
He had a very rough start, but we have worked diligently to make him as healthy as possible, and he is doing great. You would never know he has liver problems by looking at him.
Ultrasounds are not very accurate in determining whether or not there is an extrahepatic shunt. A Protein C test would help determine whether it's likely to be MVD or extrahepatic shunt.
If you do decide to go ahead with the surgery, make sure that it's with a board certified surgeon who has extensive experience with liver shunts and liver disease. A vet school is probably a good idea.
If your baby has MVD, it has to be managed medically and with dietary changes. One of the major staples for a dog with liver disease is lactulose. See, when the liver is not functioning properly, it cannot filter the ammonia that is produced from the protein and then the ammonia enters the bloodstream. If it accumulates, it will cause neurological symptoms and hepatic encephalopathy. The lactulose helps bind the toxins from the blood and pushes them through the colon.
Milk thistle is highly recommended to help the protect the liver from further damage. Do not buy the liquid kind, the capsules are better and you can open them up and dump the amount your dog needs on her food. If you need the dosages, let me know, and I'll dig them up for you.
Denosyl also helps protect the liver and is beneficial for them. If your dog is smaller, then Vetri-DMG may be better for her because Denosyl tends to cause nausea in the tinier yorkies because the dosage is the same for them as for a 10 lb dog.
She has absolutely no symptoms at all? Is she ever a picky eater or has she ever had UTIs, darker urine, head pressing after high protein meals, hypoglycemic episodes?
Also, I want to add that meat and poultry proteins produce the most amount of ammonia which makes it hard on an already compromised liver. Dairy, vegetable, soy, and egg white proteins are easiest on the liver and produce the least amount of ammonia. Small, frequent meals are recommended as well for several reasons.