All but one dead. Help. Need to know what to do with her.

I let the chickens and ducks out yesterday morning. When we got home last night, all the chickens and all but one duck was dead. We actually can't find 2 packing peanuts. They are all about 3 months old. They looked like they just dropped where they were. No signs of any varmit entering the run. No marks, just dead.

The one duck that is still alive we found under the coop. We purposely put the coop up so they could get under it for shade/protection if needed. My son had to crawl under it to get her out when he got home last night. She is still alive this morning. She is not walking. She is pulling herself around by her wings.

Do I give her more time to see if she gets better or do I cull her now? Any Help is appreciated.

No cedar bedding. I do all the feeding and watering so the kids didn't give them something they shouldn't have. The coop is nowhere near the garage. It sits at the back of the property. They all looked fine when I let them out.

My oldest DD said she heard everyone "talking" in the morning. But didn't spend anytime outside yesterday to know about when it started to occur. We got home about 6.

ETA--not cold, was in the 80's yesterday. No plants in the run.