I'm sorry for your loss.
I'm sure that
@azygous and
@Eggcessive will chime in. I'll also tag in
@coach723 for her thoughts too.
First of all, thank you for the photos, I'm sure it was hard to do. Your husband is skilled!
I'm not a vet that's for sure and any necropsy I've done is amateur at best.
The discoloration of the liver is interesting. Whether it's at a stage of Fatty Liver disease or is affected by Aflatoxins, I don't know, but the lower lobe especially looks to have started to possibly lose some function.
I also see egg yolk in the coelomic cavity which would, to me indicate internal laying.
The heart has some fat, there's also a bit of a fat pad which is not that uncommon in laying hens. Some hens are more fatty than others, but it may have been enough to deem Fatty Liver Disease, but hard to know.
Oviduct to me looks nice, I see intact ovum and no signs of cancer of the ovaries from what I can see.
If I had to guess, Fatty Liver Disease with Internal Laying. But it will be interesting to see what others say.
As for the yellow "stuff", I can't i.d. that, it's curious though.
Sometimes I've been left with more questions than answers when I do this...
Hope that helps.