Yeah I’m aware a necropsy would provide the most information. I guess I’m also wanting to hear some causes of sudde death. I’m sure there’s many. But then I can educate myself on them for the future.
I'm very sorry for your loss, what a lovely girl, thank you for sharing your photos

I agree with @coach723 without further investigation, it is hard to know the cause of death.
If you still have the body, you could try an informal necropsy, if you can bring yourself to it. Look in the abdominal cavity, intestines, reproductive system, gizzard and organs (heart/liver). You can post photos and we might be able to spot something wrong. Alternatively, since you work for a vet, ask them if they would be willing to take a look.
It is heartbreaking to lose one suddenly, but I do find it a slight comfort if I can figure out the cause - I had a pullet suddenly die when she came into lay - she had a very large egg lodged in the oviduct and from what I could tell, she ruptured her liver or spleen and died from hemorrhage.
Again, I'm very sorry.