I'm sorry Chloe, it doesn't sound good love. But if you want to try to keep her a bit warm, have you got a box you can put her in,with a hot water bottle wrapped in an old towel or something?
Unfortunately, once you can see how ill chickens are, it's usually too late to help them. I've lost loads of chickens in my time, but it is still upsetting.
You can also try a little warm water with a bit of salt and sugar dissolved in it. The salt will help if she is dehydrated and the sugar for a little energy.
Good luck love!