Sorry for your loss.
I would take the remaining kid (or it's poop) in to a vet for a fecal / well baby check.
I'd also probably give her a selenium injection, just for grins.
Has she been vaccinated w/ CDT and boosted?
We lost kids our first year to cocci, and because they were our first, I didn't really know anything was wrong, since they ate, played, etc.
Once I started treating them and saw how kids were supposed to act, the difference was amazing.