I also see some kind of little chip right where the top curves down to meet the lower beak. It could totally be debris or something, and if you say there is no damage, then I will take you at your word.
I'll be honest... I feel she looks exhausted in the first picture. Her eyes and face are tired.
Have you checked her over for lice/mites and their nits (eggs) around the base of her feathers by her vent? That's their favorite hiding place.
When was the last time you wormed your flock?
It's almost like she's shrinking into herself... I see her wattles and comb are shriveled (or flopped over... I can't tell from this angle), her face is paler, and, of course, ......... her beak......
The only thing I can think of that would be THIS advanced after only five days would be acute trauma (like a deep bruise)... Is it possible she got her beak stuck in something while you were away? A coop or run door? A window? Someone accidentally stepped on her?
Chickens explore the world with their beaks, so it's easy for them to get injured that way.
Outside of trauma/injury, I'd lean towards some type of deficiency or circulatory issue... But I've never seen anything like this.
I would separate her and bring her inside the garage in a dog crate or something similar... Keep her in a quiet, warm, calm environment. Feed her the normal ration and include some boiled egg to whet her appetite.
Sorry I can't be of more help... @casportpony, @Eggcessive, @enola... Have y'all seen anything like this before??
Edit to add: I bet her beak is tender, no matter what is going on. I might soak her food before you give it to her, so it's nice and soft and easy to pick up. :)
Edited by MrsBrooke - 3/17/16 at 2:21pm