Sadly, I agree, it looks like she's a meat bird, so her legs are likely unable to support her any longer.
She's lost all her feathers underneath her is soiled. This is usually what meat birds look like.
I do see what looks like an issue on the bottom of her feet, hard to tell if it's just caked on mud/debris or if it's bumblefoot. Swelling of the Ankle (Joint), could be a slipped tendon or blown tendon which happens with meat birds too.
I'm sorry you face this. Depending on how much time you have to dedicate to her care, you can try placing her in a sling for periods of time to get her more upright. Some folks do this to buy more time.
Everyone keeps chickens for different reasons, so culling her may be more in line with your keeping goals. Not always an easy thing to do, especially when you get attached to them.
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