sick 1yr hen - unknown cause

[Polka and Dot]

My 11 month old olive egger is very lethargic and getting worse. I noticed she was off yesterday, walking weird. Today she seems dizzy, its harder and harder for her to walk, now she is sleeping unless I come in (photo). She has poo'd 2x today and laid yesterday (already showing mild symptoms when she laid). She is a good layer so I would be expecting an egg today or tomorrow.

I've checked her head to toe, she has no injuries (I'm a newbie but I have dealt with a hard to find injury already). This is the normal colour of her comb.

No signs of respiratory anything. My other 5 hens are totally fine. Feet are good. Vent is good.

She's been isolated inside since this morning. I've given her some water with Manuka in it and she has eaten a fair amount of egg.

I don't know what it is or what to do.

Edit to add: her tail is down and her wings are kind of hanging. Can she be egg bound even if she laid yesterday? She lays tiny eggs and once had a huge double yolker.

 

[BlindLemonChicken]

What does her poop look like? How long have you had her? Have you added any new birds lately?

 

[Polka and Dot]

The poop is that normal but gross kind. A little watery but not too alarming. Has been normal until today.

No new birds. I've had these 6 and only these 6 since they were 5 days old. I am pretty careful with biosecurity. The wild birds are around sometimes, but hens' food and water are cleaned daily.