It does sound like she needs a vet ASAP.
In the meantime, it may be beneficial to bring her into the house in a dog kennel or something comfortable that can have a blanket base. Putting that cage in the bathroom with the door closed and the shower on high can get some helpful steam into her if she’s having trouble breathing. This is just a bandaid though. Without knowing what’s actually happening with her it’s hard to say if this will do much good.
I do recommend with how she looks to bring her in though. Any predator, rats, raccoons, etc will attack before a hen is gone. Even ants (which I’ve had to save a hen from before and shocked me) will quickly swarm a very sick hen that is unable to move quickly away.
What is the weather like where you’re at? My hens get susceptible to illness when it’s chilly because we live in the desert and they’re used to 100+ degrees. However, many hens can get ill if there’s a sudden temp spike as well.