I thought this little one had poop stuck to her feet, but upon further examination and a soak in diluted Dawn and Epsom salts it doesn't seem to be dissolving. Now I'm worried.
Looks like Pododermatitis.
Keep the chicks bedding clean and dry.
You can still soak the feet, but I would use Chlorhexidine in the water. Make sure you dry the feet really well before putting her back in the brooder.