I am so very sorry. I was crying as I looked at the photo you just posted of Princess as a puppy.
She was beautiful.
I'm glad the vet is doing the autopsy. If it was Parvo, you need to be very concerned about other pets both now and in the future. If it was rat poison, oh my, you need to know that too and figure out where it came from.
My Gizmo ate some rat poison when he a curious puppy, but luckily we caught it at the time and rushed him to the emergency vet, so this hits very close to home for me.
I am so sorry.