Weak, crying pullet :(

Hi, I need help figuring out what is wrong with my 6 week old Dark Brahma pullet, Duckie. A few days ago I found her with her wing twisted underneath her and extremely weak. I brought her inside to recover and placed a companion with her. Long story short, Duckie seemed to be interested in eating and drinking, but even now her appetite is starting to decline. She is not gaining weight, but her crop usually has something in it. Her poop is varied, she has solids and runny yellow watery poop. She is weak and stands with ruffled feathers, huddled, eyes closed for the most part. She is always wanting to burrow underneath her companion. The worst is her loud, sad cheeps. Duckie is obviously in discomfort and crying out to her mommy (me). 

More info: Got her and 17 other chicks from a co-op at one day of age and hand raised them in brooder. One chick was introduced from my own flock within the first week that was rejected by it's mother, no side effects in any of the birds. She had been staying with all 18 of the other chicks outdoors since they were 4 weeks old. Living in confined pen made of wood and chicken wire on the grass. Have not been exposed to my older birds. She had webbed feet but I separated the toes when she was 3 weeks old, no infection or side effects. I just had my own baby one week ago and so between being 9 months preggo and being in postpartum recovery I haven't been very thorough with cleaning their water (hangs head in shame).

Is she sick? Parasite? Is there something I can give her to perk her back up? Should she go to vet? Please help ASAP, Duckie is a special bird to me and I don't want to lose her!

Thanks, abbey808, I appreciate that you took some time to respond. I would've answered sooner but our internet went down last night. Sweet little Duckie just passed away this morning, but it was quiet and peaceful. I'd still like to know what caused this, in case it happens again to another bird.

In answer to your questions:

Is her condition related to an injury to her wing?  
At first I thought so, but I think her lack of thriving actually contributed to her odd position--I think she may have fallen over and/or got trampled by the other birds by accident and was too weak to get back up.

Are there any other symptoms such as coughing, sneezing, bubbly eyes, labored breathing...  anything respiratory related?  
No respiratory issues.

Does her crop empty after she eats or does it appear to be impacted?  
No impacted crop. I gave her some fluids via syringe and it seemed to pass right through her. First I gave her a watered down mix of a bit of B-complex (stuff I had been taking during my pregnancy) and a protein smoothie juice I got at Publix, in hopes to boost her energy. Then I gave her a bit of poultry electrolytes.

Any odd smells coming from her?  Any external signs of parasites...  mites, lice etc?
No external parasites could be found. Her poo had a strong stink, though.

I'll post pictures soon, maybe that will help.

These last three pics are of Duckie just a couple hours before she passed. Shelley stayed by her side until nearly the very end. Both birds are from the same flock, same age, got them at the co-op.

Thanks, Maev. She matched all but 4 of the symptoms. Initially I ruled out the cocci because I thought there had to be blood in the stool. I'll look into the Corid.

Thank you all, for the condolences. It's hard with any pet, but doubly so when it's the death of a baby! This is the fourth baby I've lost, but the first loss from the flock of chicks that I purchased (the other three hatched at home). I'm beginning to suspect that at least two of them also died from cocci. The last chick that died, Phyllis, was really tragic because I'd nearly lost her once, been treating her for splayed leg, she regained strength and vigor and seemed to be fine. I left around 10 or 11 am from my house to birth my son, and my dad found her dead that very evening 

I too, am glad that Shelley was with Duckie. She seems to have the comforter personality, so that's why I picked her. I always make sure that any ill or injured bird has a companion (unless the situation is too risky for either bird to share company), because they are more likely to die when completely isolated. What's amazing is that when I let Shelley come out of the carrier, she immediately flew onto my shoulder, hopped on top of the carrier, and nestled right next to Duckie (those pics are not staged!). 

No, they are not on medicated feed right now. I've been calling all the feed stores I can find for Corid, the closest store that sells it is about a 40 minute drive away. For now, I've disinfected all the feed and water dishes with diluted bleach, kept the water fresh, and mixed in powdered milk with their crumbles to flush out any nasties (it worked, found some red stuff in their poo the next day). There's another feed store that is closer that carries Sulmet, but I've heard mixed reviews on that stuff. So I'm going to try to get the Corid tomorrow, goodness knows I can't put this off any longer!