A post-mortem was done by Dr. Erica Miller at Tri-State Bird Rescue & Research in Newark, DE, and cause of death was probably aspergillosis, a respiratory infection that was probably worsened by stress and thin body condition. Additional testing should confirm this, as well as test for exposure to West Nile virus and contaminants.
So sad. That's what Rhea Mae & Tiago's Kate died from last year. As I recall she came to ground once and health check seemed OK so she was released. The next time she came down it was finally apparent that she was ill.