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The fact she has loose droppings may indicate that the problem is within either the gastrointestinal tract or the urinary tract as birds droppings are made up of urine and feces- if its generally just a sloppy motion without a solid center this usually means an intestinal issue.
As she has been wormed then its unlikely parasitic- but could be bacterial or some other form of parasite (such as coccidiosis).
I would isolate her from the other hens, be sure she is taking plenty of fluids, encouraged to eat, and i would really advise a veterinary exam- as i think she may benefit from some antibiotic therapy which you will need a prescription to obtain. Free range chickens can pick bacterial infections up from feeding in areas where wild birds have been.