Sorry to hear about the diagnosis.
The Vaccine does not prevent birds from becoming symptomatic or from having an infection from the virus. The vaccine may help prevent the formation of tumors. Bottom line, vaccinated birds can certainly end up sick, have issues with balance, etc. etc. This site if loaded with threads of sick birds that have been vaccinated.
Do the best you can. Treat symptoms. Vitamin therapy and see that they are eating a good all flock feed. Keep on top of parasites both externally and internally. Hopefully she will come around.