What's wrong with this Buff Orphington chick from IFA?

[4 ever Orpington]

We first got this batch of chicks to be friends with the two chicks we managed to hatch. Matilda, this Buff Orphington, seemed fine then. But perhaps I didn't notice if something was wrong because at the time we had two other chicks that were not doing well at all. Since we had to say goodbye to those two, I've noticed Matilda is low on energy. She peeps a lot and keeps her eyes a little closed. Neck rarely extends. She does eat and drink of her own free will but not much. She's growing, but not as much as Miss Honey (pictured in back for comparison)View attachment 1321029
More pictures attached. She never had pasty butt. And at first she was much better off than the runt Easter Egger but now that's not the case.

Any diagnoses or ideas on how to help? I haven't seen a chick like this in all the years I've raised them. It's been about a week with no improvement (but at least no worse either)

I’m sad for you and that sweet baby.

 

[EurekaPaprika]

She keeps going up and down... Some days she seems good, other days she seems really sleepy. She's growing a bit, but now she's smaller than our runt.