We could help you better if you could give us a little more information, please. If you could answer the questions in this sticky
https://www.backyardchickens.com/forum/viewtopic.php?id=3569 into this thread, that will help us get a better idea of what's going on with your pullet.
In the mean time, make sure this pullet is separated and can get to food and water easily and is eating and drinking.
Also examine her carefully. here are some guidelines - the more information you can give us, even stuff that seems silly, the more information we can provide back.
Examine her weight; is she thin, heavy, skinny, lumpy, fat?
Examine her eyes: are they clear and bright? Pupils both round and reactive to light?
Examine her beak: are her nares (nostrils) clear? Is the inside of her mouth healthy and pink? Does she have excess mucus? Is her beak pale in color?
Examine her crop: Is she holding feed after a night of not eating?
Examine her skin: check carefully for lice/mites (see below**). Look for any broken skin, redness of vent, scratches, anything abnormal.
Examine her abdomen: Feel delicately between her legs and back up to her vent - do you feel any lumpiness, or is she firm, or is she hard?
Listen to her respiratory system: With your ear against her throat and chest, listen to her breathing. Do you hear hiccups, wheezes, rales, or rattles?
Examine her vent: Other than the clinging droppings, do you see white or black waxy stuff near her vent? sores from the droppings? (clean and treat and dry them). Is her actual vent opening tight and dry, or is it dilated (open) and moist. This can indicate if she's trying to lay.
Tell us more about diet: do your hens have access to both granite type grit as well as oyster shell? Is she on a laying diet for 95% of her diet, grains less than 5%?
Worming: do you worm?
Environment: does she have access to any compost, kitchen scraps, manure piles, ponds? Is her bedding dry and clean? What is the area like where she free ranges?
Thank you for answering all million of these questions (wink). I look forward to your reply.
**Mites and lice: they're nearly microscopic, and mites only go onto the birds at night often enough and then occassionally they just remain off the bird while they lay their eggs in the wood of the coops, etc. Check them at night, with a flashlight (and the coop light on), and a light colored pillowcase to help you find mites. Ruffle through all of their feathers. Pay careful attention to the warm/moist areas under the wing feathers, near the vent, along all the feather shafts, etc. If you find them, you must treat the bird and the premises and the birds must be retreated at least once in 7 days - preferably twice. Recheck a few times this week and next to try to find mites. Let us know if you find anything like this and we'll advise on treatment.