lethargic bird - I am a novice laying chicken keeper

[birdginia]

I have seven six month old birds, moved from a small local farmer about two weeks ago. All has been going well until this morning. I have one girl who did not leave the coop - I checked on her a couple of times to she if she was busy laying, then noticed her struggling to move when I disturbed her. Brought her in house and tried to see what was going on with her but was afraid to stress her further. Gave my birds left over popcorn yesterday - wondering if that is a big no-no for chickens. Is there a list of what NOT to give chickens. Help and thank you in advance!