Chicken breathing very heavily

[RaintheRooster]

Will treating her even if she does not have worms make her sick?

 

[pwand]

Will treating her even if she does not have worms make her sick?

Have you had her poop tested for worms? How do you know she doesn't have worms?

 

[pwand]

@RaintheRooster
Worms can kill a bird. You can not always see worms. Did you treat for mites and lice as well.

You need to rule out problems:
Have you checked her for egg bound?
Messy vent feathers can be vent gleet.
Sour crop or impacted crop.

Heavy breathing is not a good sign, hens can get egg yolk peritonitis / internal lay, they can get tumors, cancers. There is so many possibilities. You need to try to figure it out by ruling things out.