Can you take photos without the red light?
Does the radiant heater emit red light or are you using a red heat lamp as well?
Photo of the whole brooder/housing may prove helpful.
Dry poop, the chick may be getting constipated. Watch to see that she's staying hydrated. If you need to, give...
I'm sorry for your loss.
Chick grit is usually crushed granite. Chicks and Chickens eat a few pieces and the grit is used in the gizzard to process foods/material that they bird consumes.
How is the other chick doing? Photos of her and her poop?