I'm sorry for your loss.
If you happen to lose another one, send the body to your state lab
https://nhvdl.unh.edu/tests-fees-forms It looks like you need prior approval to send a bird/specimen in, you can find out by calling 603-862-2726
I agree, I would not mix the grit and oyster shell with the feed. I put mine in small containers that attached to a post in the run, they will take what they need. We all love to give "goodies" to our flock. Everything in moderation. Since they do get to free range/forage some in the afternoons, that is great. Personally, I would cut out the bread. Mine love the fruits/veggies too, I would take a look of just how much they are getting, but generally they won't overdo on those unless they hate their food. A little scratch goes a long way - if you have a hard time getting your girls to come in at night, either lock them up for several days in a row to retrain them where "home" is or teach them to come with your scratch (remember - just a little - about 1tsp per bird). Put your scratch in a can that you can shake - this makes a nice noise they will recognize in no time - shake your can and call them, once they are all in the run, reward them with their scratch

This comes in handy anytime you need to get them to come, not just at roosting time.
Here's Terry Golson of HenCam calling her ladies