How old is chick? This does sound like chick is dying,pick her up,open her beak look for anything stuck in throat. Has she been ill? What is she eating? Could be anything,are any other chicks looking ill? Look up symptoms for Coccidiosis in the event this is what it is. Just hold her and snuggle her until she passes,let her know she is loved.
If she is let out or given treats she needs grit. Did you look into her mouth? If she has shavings in her brooder,she may have ingested a piece.
I would still look at symptoms for Coccidiosis,very common in chicks and can hit at any time. Cocci is a parasitic infection of the intestinal tract,spread by droppings,which get into feed/water via droppings. Some symptoms are runny/watery poop(may or may not contain blood)fluffed feathers.lethargic,not eating/drinking properly. Cocci can kill very fast,watch other chicks if they have even one of these symptoms,purchase Corid(amprolium) dosage for Corid 20% powder is 1/2 tsp per gallon of water,dosage for Corid liquid 9.6% is 2 tsp per gallon of water. Treat all chicks for 5 days,do not give vitamins during treatment(interferes with medication)give vitamins after. Treating chicks for Coccidiosis will not hurt them,but not treating(if they have Cocci)will probably kill them.
