Sick or injured chicken... help

[JoeST]

One of my hens is either injured or sick. I don’t see anything that indicates she’s been hurt, but she’s breathing heavy & fast & stays almost limp if you touch her. She is normally the only skiddish bird out of my six. I walked right up to her pet her & picked her up without the slightest fight.
I’m not sure where to even start to narrow down the problem & all my other girls are acting completely normal. Any help would be appreciated!

 

[JoeST]

I’ve separated her from the flock & given her a separate box with a heat light. After being in there for a bit she at least seems to be a bit more alert. I thoroughly maybe she had an impacted crop after some reading but her crop feels empty. Not soft or anything just empty & flat. Normally in the evening all the girls have a pretty full crop.
I’m not sure if she’s layed either as recently most of them have been a bit random & I’m not home most of the time when they lay to know for sure who’s laying & who’s not. Her vent does look normal & clean.