I think you will be able to tell a lot by having the bile acids test done. It should be done as a pair of blood tests: fasting and post-feeding (post-prandial). The ammonia test is helpful, but not essential. The L/D diet helps to control the protein level she is eating, so it usually helps, since one of the by-products of protein digestion is ammonia, and it is ammonia that is most likely the substance that is causing her unusual behavior. Smaller meals, frequently, instead of larger, less frequent meals, should help prevent an "ammonia rush" that could occur after eating a lot of protein. The "catch 22" of protein restriction, however, is that the liver supplies the body with albumin, the most important protein component in the body. It transports many import chemicals in the body and is the main substance that regulates the fluid component of blood. Restricting protein intake too much can cause albumin to drop. Therefore, the protein that she does take in should be of the "highest quality" possible, in terms of amino acid (protein components) composition. Milk protein (casein) and egg protein are very high quality proteins, and I believe that L/D is high in the percentages of these. Do you remember whether the albumin level in her blood was lower than normal? Was her blood glucose normal?
I do think that there is hope for her. The fact that she is already 7 years old is in her favor. If the surgery had not helped a lot, she would have had many more problems early in life. If you can take her to an internal medicine specialist, who can help you tailor a maintenance program for her, that would be ideal. There are some supplements available, like Marin, and Denosyl, that sometimes help support liver function. The internist will probably do an ultrasound of the liver. I doubt that a visit to the surgeon would be all that helpful at this point, because you are probably not dealing with something that can be treated surgically.
Just one additional thought: It would still be wise to see a neurologist. One shouldn't just assume, since she has had this major liver problem in her life, that all subsequent problems will be caused by it. It is possible that her odd behavior could be caused by something else.
I have some other obligations today, but I will check back in this afternoon.