Why did her chicken die?

So my friend has chickens, (not very well taken care of honestly, I will be taking them soon), their coop gets cleaned and they get fed, but just could use some more care. Anyways, their chickens are about 2 years old, one Americana hasn't laid eggs for awhile, about 6 months or maybe more? Unless she for some reason started laying brown eggs. Another laying chicken had died, before she died my friend said she was losing feathers (I have young birds right now, so I don't know what the molting process is), later I found her dead inside the coop, she didn't have bugs on her, and I didn't see blood. So I'm just wondering what the cause is. They get fed layers feed and household scratch.