I too suspect that it was probably reproductive based on the symptoms and there is likely no risk to the rest of your flock. Again, very sorry for your loss, and completely understand about the kids. Mine when they were small would not have remotely understood doing that to a pet.
I'm very sorry for your loss. :hugs
If you are up to it, and curious you can do an informal necropsy and post pictures here, and maybe get some better answers on what may have been ailing her.
I can give you links, or you can search for instructions. It's not difficult really, except maybe...
Just saw this, so first, great informative post by @Hen Pen Jem!
I agree with the assessment on the oregano, I've used both leaf and oil, but it has never been helpful with a bird with this degree of illness. I wish you the best, but know that not every bird with this degree of illness can be...