I'm sorry for your loss.
This question is intended to narrow down the possibilities that might help the rest of your hens in the future: When you say yellowish/white discharge that smelled like cheese, was that from her mouth or from her vent?
Excellent thought, @msiler - checking for parasites by the vent and top of the tail is another good practice. If it is mites, Elector PSP does a really good job, but it is SPENDY. A little goes a long way - it's used as a premise spray too. Looking under the roost, visiting the roost at night...