Your first picture of your chick, on her back, made her abdomen look swollen. As if she were a "mushy chick". In the second pic, lying on her belly, it wasn't apparent.
I had 3 "mushy" chicks in an early hatch, and they couldn't get upright. They'd fall on their backs. They also had cushion-bottoms & extra-plushy down from swelling all over.
They didn't want food or water for the first few days. Does her bottom feel heavy for her?
If she doesn't fit any of that description, she's probably not "mushy" --which means inflammation of the umbilicus with G.I. swelling.
If she has a little mushiness, it may pass in a few days. I have three beautiful hens who got through an extreme bout of "mushy" and are fine.
If you have a little water soluble antibiotic you know is specific to this type of disease, you could mix it with water & eyedrop it --if she's mushy.
Another of my mushies' symptoms was panting at the 95 F brooder temp, I guess from fever.
Sometimes they just have dark green poop at first... It might be digested yolk sac. It also might be a sign of fighting infection.
My mushies had this color poop when they finally pooped. I've had some who did it with no sign of problems.
It comes out grain-colored when they start eating grain.
Sometimes, they're just weak from coming out, especially if it took her longer.
If she's been out 36 hours & still can't stand up, then I'd start to worry. She may just need to rest it out her first day.
A little electrolyte mix --Pedialyte-- with water in an eyedropper might help her get her strength back.
Their toes are frequently curled up from their position in the egg & won't straighten out until they've been walking on them a few hours.
I hope this helps. I don't know a lot, but my mushy chick experience is vivid still & I want to help someone else through it if this is what you have.
Good luck!