Hen can't hold head up. Need advice.

[buckabucka]

I have a 2 year old Buff Chantecler. Yesterday, she spent quite a bit of time in the nest box, and now she is exhibiting the following symptoms:

Lethargic
Diarrhea
Can't hold head up (her head slowly drops, she picks it back up, and it slowly sinks again, a bobbing motion)
One eye will not open all the way
Appetite is good/regular ( eats layer feed)
Comb is very bright red (seems brighter than normal)

Treatment:
We examined the hen and found lots of mites. Dusted with DE, and plan to purchase permethrins. Hen is isolated in cat carrier in our house. Given water with Avia Charge, layer feed and scrambled egg.

Questions:
Could all these symptoms be caused by mites, or is there something additional going on? (the stuck eye and diarrhea raise questions).
Has anyone ever successfully treated mites with DE and/or permethrins? We are hoping to avoid using Sevin.

I don't think this hen has been laying eggs, but we have many hens that lay eggs the same size and color, so it is hard to judge. She certainly has not laid an egg today in the cat carrier.

I appreciate any advice or speculation about her symptoms! We would like to treat this ourselves (not at a vet).
Thanks.