Oh Oz that is terrible! I am so sorry you lost so many birds!@getaclue
Sorry I am jumping in late again regarding your run in with coryza.
You were lucky she told you that the chickens were infected but what if she didn't or did not know?
Its so easy to bring something home that will infect your birds from visiting someone.
Routinely practicing sound biosecurity is important. It's a bit like safe sex.
You sleep with everyone they slept with.
I seeded my father in laws flock but now won't even go and see his birds. I tell him to show me pictures.
Coryza is endemic in the Phil's. I vaccinate at 8 and 11 weeks. The vaccine is 500 doses but it keeps.
Recently I got hit by an illness that killed 50% of a grow out pen with 16-20 week birds overnight and another 25% over the next three days. All in 60 birds that were essentially presold at $50 each. They had no symptoms except torsioned neck.
We think it was some strain of Newcastle disease. That pen was missed in vaccination rounds with a change in staff. A tough lesson.