I'm glad that she's improving, and they are doing better.
I'm also glad that you added a couple of bowls of water. Hopefully this will be helpful in addition to all the other things you have done. Chickens like to drink deeply so bowls are a good choice. While the drinking cups can stay...
I'm sorry for your loss.
Can you post photos of your coop/run, water and feed stations?
Photos of pullets and their poop too if possible.
What do you feed, including treats?
I agree, it sounds like heat exposure. Giving the Corid won't hurt, especially since you saw bloody poop.
If you lose...