The breeder I obtained her from says no, that isn't true. I am very concerned that this is a fatal problem. I just heard from another of the vets to whom I sent Belle's information. He recommended that you get a second opinion before allowing any further treatment. It was his opinion that a liver biopsy should have been the LAST resort after all other tests had been exhausted.
Second opinions are always a good idea when in doubt about the choice of tests and treatment.
Ask the breeders in your area about the vet that they use for their birds. Breeders usually know which vets know birds and which vets to stay away from. Try not to worry about it being a fatal disease because birds are much more resilient than they appear to be. Also, there are many reasons for her behavior and test results other than fatal disease. As to whether a breeder can know from the beginning if there is a problem, I do think that a breeder would know that what you describe is not the way MOST healthy Eclectus babies behave.