Have you disposed of the body? If not, I suggest you do an exploratory necropsy. More simply, you just cut open the body cavity where the organs are and look for anything strange.
Was this hen acting normal prior to your finding her in the front yard? Or had she been hanging out a lot in the nest, not wanting to do her normal scratching around outside?
I suspect she may have had Egg Yolk Peritonitis. In this disease, the eggs get diverted to the abdomen and accumulate there causing infection. It's this infection that kills the hen eventually. While I've never heard of a hen vomiting the contents of her stomach cavity, it might be possible she regurgitated upon dying since the death throes of a dying chicken are often violent.
There is another freaky possibility, and this actually happened to a hen of mine. I had a can of wasp spray sitting beside the coop where the chickens liked to hang out underneath. The rooster was outside and he somehow was dancing around and hit the trigger on the can, spraying the hen in the face, killing her.
When I found her, she had yellow, yolk-colored goop coming out of her beak and nares. While the wasp spray wasn't yellow, it must have reacted with her bodily fluids and created the yellow goop as she died.
Would it have been possible that your hen made contact with insecticide as it was being sprayed? Could kids have been playing with a can of bug spray and decided to see what would happen if they sprayed it in the face of a chicken?
I have had a hen choke on something right in front of me, however. They do panic and run as they can't breathe, but they quickly collapse. If she was a significant distance from the coop, I doubt she choked on an egg. And it would be pretty hard for her to choke on raw egg. I think you should look at other causes for her death.
I'm so sorry you lost her.
