Welcome to Yorkie Talk. Sorry to hear Roxy's test are indicating a liver problem.
I went through the exact same thing with Tiki, finding abnormal liver values upon a pre-spay blood test at 7 months. Ultrasound does not always show shunts, unfortunately. I ended up waiting and retesting after her first heat, , and they went ahead cautiously with the spay after 1 yr old. It was felt that she likely had MVD, however I opted not to do a liver biopsy during spay, per my vets advice, because it involves a much longer incision and longer anesthesia time (which is hard for a challenged liver to process) and additional chance of infection. We decided instead to assume she had MVD and manage with diet and supplements.
I am happy to say that Tiki just turned 6 and is doing just fine. She does well on any moderate to low protein food, and only gets sick when somebody gives her a fatty snack, which her liver cannot process.
The link Maximo posted is very good, and the brochure is a great overview of liver disorders:
https://vetmed.tennessee.edu/vmc/Dow...NAL-201304.pdf
Good luck and keep us posted.