No, please don't have a liver biopsy done!
What tests has she had done so far? Bile acids? What were her numbers?
The protocol for diagnosing liver disease is first a bile acids test, then a Protein C test, then a scintigraphy. Don't let anyone tell you to get a biopsy done or waste your money on an ultrasound as they are only 80% accurate at best.
Unfortunately, most vets just don't see enough cases of liver disease in their practice to know how to diagnose and treat it. Are you close to a vet school?
Here are some links for you. If you scroll down to page 10 of the first one, you will see a flow chart of how to diagnose liver disease.
http://www.idexx.com/animalhealth/an...r0905final.pdf Hepatic Vascular Disorders - WSAVA 2006 Congress Portosystemic Shunts FAQ