Hi there! I finally found the thread.
How's she doing?
Since she hasn't layed yet, I wonder if she's eggbound, though doubting because I don't think she would have survived this long. She could be a young chick that hasn't ever layed, and she could be an old chick that doesn't lay.
The diarrhea, if you see bright red bleeding, she could have coccidiosis, and/or worms. Not sure about the undigested food in the diarrhea, but sounds like it is passing through her system too quickly. I'll try to find out why. Do you have grit available for them?
What feed are they getting?
Is she still eating and drinking?
Since it's been awhile since she has been wormed, I would either take a sample to a vet and asked if they would do a fecal to see if she does have worm, or if that isn't a possibility, I would worm the whole flock. Chances are if one has them, they all do.