Hi, welcome to the forum. Glad you joined.
Can you tell us a little about your flock? Age, are they laying, any males, do they forage or are they confined to a coop and run? What size coop and run? Did you check her body for injuries? Did you noticed her acting different? Things like that.
Chickens can die for a lot of different reasons; predators, other chickens, disease, injury, poisoning, laying problems, or birth defects just to mention a few. Sometimes you can tell they are not feeling good, they can stand around puffed up and not eating or drinking. Or it can be sudden, you just fine them dead with no warning.
It sounds like it was sudden and you did not mention any noticeable injuries. It is always possible she ate something that killed her suddenly. That doesn't necessarily have to have anything to do with that block, but it is something to consider. That block was not in your control until you got it. You don't know what happened earlier.
I'd probably get rid of it just to be safe though it is not that high on my suspect list.
I've had hens die due to injury. For example, one broke her neck. I think she was trying to get away from an amorous rooster and banged into something though it could have been from something else. I've had hens die from what I think was a birth defect. I think she had a defective heart and died of a heart attack. I've had hens die in excess heat, over 110 F (43 C). I think there was something wrong with these, they were not acting right before they died. a little lethargic. These are the things that come to mind when one just falls over dead.
