Pullet: broken/dislocated knee? And what else is going on?

I'm not completely new to chickens, but I did not previously have any problems - I was given a small flock of adult laying hens, and kept them without any trouble for nearly two years before moving to GA.

I've got a 4mo FBCM pullet who started limping about a week ago. It seemed to get worse, so we brought her inside. The joint at her right knee is very warm to the touch. She puts practically no weight on the leg, and the limp has become more pronounced.

Although she is eating and drinking, she is obviously getting worse. All day long, she seems to be dozing - like she cannot stay awake. Whether she is in the small box we have her, or on the small perch/roost nearby, or just on the floor, she is dozy. We've noticed blood (not bright red - more like a pinkish-red thin worm-like strand) in her stool today. I noticed it a few days ago, too, but it looked more like the picture from that poop reference site that indicates it could just be intestinal lining being shed, so at the time, I didn't worry.

A few days ago I had a 4mo buff orp pullet die, possibly from Marek's, but I do not know. (I didn't know about Marek's until someone mentioned that the symptoms seemed similar to hers before she died.) I've lost two other pullets in the last month, at least one of which I thought might be from high heat. and humidity The other one also had a limp, but she'd had an injury to her leg which we thought explained that. I have, twice, treated these young birds for cocci, since a couple of them showed symptoms.

A couple of things I know:

- The feed (a non-GMO feed from Resaca, GA) I had been giving them is no longer carried by the feed store where I usually shop, because of quality issues. I found this out about 2.5 weeks ago.
- I bought chicks from two sources: a local hobby farm, where none are vaccinated, and a local feed store, which presumably gets their chicks from a hatchery. I don't know which one, so I don't know if they're vacc'd.
- My property used to be part of a farm a good long time ago (maybe 30 years ago?); I know that, at least on the adjoining piece of land, there was a big commercial poultry operation, because my neighbor said they found the poop pit when they were excavating for her basement. I don't know if my property had poultry on it; I just know that a "'round-the-corner" neighbor said his grandfather used to plow the fields here.
- I started with about 36 chicks, and have lost five so far far - the first was a 2wo salmon faverolles from the farm, the second and third were rare breed chicks from the feed store, and the fourth and fifth were also from the farm. This sixth one - the FBCM pullet above - is a farm chick.

I don't know of any local vet who treats chickens, but I hate to see this little girl suffer. I don't know what to do! Help?

 

Vitamins! Oh wow, I hadn't realized.

To my knowledge, no one near me - at least, no one I can see - has chickens. From reading this evening, I know it can be wind-borne. How heartbreaking to think this is a vitamin deficiency issue. I'll head out to TSC first thing in the morning. If I recall correctly, I've seen gold packets with the vitamins you mix with water. Is that the same as the nutrient drench I've also seen?

I bought one bag of the TSC brand of feed about a month ago to mix with the non-GMO feed, since I'd been told it was "coming in soon", and they are now on Countryside Organics feed.

Thank you so much!