Hmmmm....from what you describe, I think you have a sick chick. I'm sorry. Hopefully this will be mild and pass quickly. Was it especially hot today?
I would immediately put her on something like Save A Chick (vitamins and electrolytes) while you figure things out. [Is she still eating and drinking?] And I would separate her from your other chicks.
At 8 weeks , my mind thinks of Markes, coccidiosis, or viral/bacterial/fungal respiratory disease.
There is no paralysis, so Mareks is unlikely (thank God).
The poo is probably normal. It does not look red enough for coccidiosis to me (which is frank blood in the poo) nor watery enough for diarrhea.. The photo looks like it could be normal cecal dropping with some shed intestinal lining (normal)....so I'm not thinking yours has coccidiosis. Also, coccidiosis would not cause squeaking/vocal noise/breathing noise (rales) nor moist nose. Keep watching the poo to see if blood is in it or if it matches any of the "sick" poo. (See chart linked below).
Listless with vocal noise (squeak, nick, rattle) and moist nose indicate a respiratory illness as likely.
Having been kept inside, assuming you keep a clean brooder (no mold growing, fecal build up, etc.), and that you have no other birds with symptoms which you could have transferred agents from... it could be CRD (bacterial caused Chronic Respiratory Disease) as that can be transferred from hen to egg.
If it is CRD, or another bacterial respiratory infection, an antibiotic would be in order. You can get antibiotics at the feed store or your vet.
If it is viral, antibiotics won't help. Newcastles and IB fit into the category. They can be transferred through the air from wild birds, beak to beak, droppings, feed bags, anywhere a virus can hitch hike. With viral, you cross your fingers and hope it goes through quickly with as little damage as possible as there is no treatment for virus infections (like our common cold). If it is viral your other chicks will almost certainly catch it as morbidity (those affected) is usually high, however, good news, mortality (death rate) is low so most survive and go on to happy lives again.
I battled my flocks viral IB with Chick Saver vitamins/electrolytes, Elderberry tincture in the waterer (antiviral), fresh garlic in the feed (boosts immune and antiviral), and then followed up with a week of Rooster Booster Triple Action which has a wormer (Hygromycin B) and Bacitracin (antibiotic) which commercial growers use in continuous feed for CRD.
http://www.abetterchicken.com/product/50101
EDITED TO ADD: Often it is good to follow up with antibiotic after viral as secondary bacterial infection can set in with the extra mucus the viral infection creates.
I've posted some links below to help you figure things out.
Good Luck,
Lady of McCamley
Poo Chart of healthy vs. illness (Compare your poo to one of these)
http://chat.allotment.org/index.php?topic=17568.0
Respiratory Illnesses in Chickens (Very likely one of these due to moist nose and noises made with listlessness)
http://www.barnyardhealth.com/resinindompo.html
Coccidiosis (I don't think likely as I don't think the poo is bloody but rather normal intestinal shed)
https://www.backyardchickens.com/a/coccidiosis-how-to-treat-it
Mareks (not likely as your bird is not showing paralysis)
http://www.thecuckoopoultrystudofaustralia.com/mareks-disease.html